Most of the important settings can be easily changed within the actual in-game settings screens. To access this area, start up UT2003 and click on the Settings option. You can also access settings during a game by pressing ESC and clicking on the Settings button. There are 11 settings screens. Each screen and its associated settings are covered in detail below:
Resolution - This setting determines how many pixels (the individual dots which make up a computer image) are displayed on the screen. A resolution of 800x600 implies 800 pixels wide by 600 pixels high on your monitor. Obviously the higher the resolution (the more pixels), the more detailed and clearer the game image, but it takes more graphics card and CPU power and hence you will see less frames per second (fps). The highest resolution available in this list of resolutions is limited to what your graphics card and monitor are actually capable of rendering (drawing on screen). The resolution alone will have the biggest impact on your framerate, along with the texture settings below.
Color Depth - This determines how many different colors can be displayed on screen. The two options are 16-bit and 32-bit, with 32-bit only shown if your graphics card supports it. 32-bit color looks the nicest, with 16-bit color showing more color "banding" - that is, the gradation between colors is more apparent. 32-bit color also resolves a lot of problems with flickering and missing textures, especially in OpenGL mode. However 32-bit color requires a bit more power than 16-bit, so if you need more fps, switch to 16-bit.
Full Screen - Tick this option to run UT2003 in full screen mode, for the least likelihood of errors or crashes. If unticked, UT2003 will run in a window on your Windows desktop and this may cause problems.
Gamma, Brightness, Contrast - While I could get technical here, for most people there is no real difference between Gamma, Brightness and Contrast. In effect these three settings affect how bright (washed out) or dark your image looks. Set these to taste. I recommend setting the Contrast to 1.00 first. This ensures the crispest image on your monitor. Set the Gamma to 1.00 also to begin with. Next change the brightness until the picture appears to have natural lighting and text is clear. Then go back and tweak the Gamma and finally, if necessary the contrast until your screen is not too washed out and not too dark. It really depends on your monitor's brightness/contrast settings as well. For reference, I have a Brightness of 70 and Contrast of 100 on my monitor, and a Gamma of 1.00, Brightness of 0.77, and Contrast of 1.00.
Texture Detail - This determines how sharp or blurry the in-game textures (the images that form the surface of every object around characters) will look. The options range from Lowest to Highest. The higher the setting, the slower your fps. Settings of High and above ideally require a graphics card with 64MB of VRAM (Video RAM) or more or you'll notice a lot of stuttering as textures are loaded back and forth if your VRAM is less.
World Detail - Options range from Normal to Highest, and in turn determine how many objects from your surrounding are displayed. The higher the setting the richer the landscape, but the higher the computing power required (and hence the lower your fps) especially on levels where you can see further and/or there are more objects to see. If you have an older graphics card in particular, lower this setting to improve your fps.
Character Detail - Similar to the Texture Detail setting above, from Lowest to Highest this determines how blurry or sharp the textures on all the characters look. The higher the setting (and the more characters on the screen) the lower your fps. As with the Texture Detail and World Detail settings, choose High or greater only if you have a graphics card with 64MB of VRAM or more.
Physics Detail - Changes the level of detail for the simulation of physics in the UT2003 gaming world. The higher the setting the more CPU effort required to crunch the numbers to show more realistic effects ranging from the basic "ragdoll" effects through to effects such as water ripples. The settings are Low, Normal and High, and I would recommend that the slower your CPU (i.e the closer to the 1GHz recommended spec), the lower your Physics setting, as this setting can really affect your fps.
Character Shadows - Ticking this option allows each character to cast a shadow on the surroundings. This adds to the realism but also affects your fps. Turning it off will remove the shadows but improve fps.
Dynamic Lighting - Ticking this option allows the various lights in the game to react realistically with objects, shining at different angles off weapons, characters and walls based on the light's position. This makes for great effects but can decrease your framerate, so untick it if you need more fps.
Detail Textures - Adds a level of detail or "grain" to the textures which makes them look much crisper when examined close up. However this can reduce your fps, so untick for more fps if necessary.
Projectors - Projectors covers a range of images projected onto textures, such as shadows from characters and objects (like tree shadows) and decals (see below). The noticeable effects of unticking this option include removal of such shadows and decals, even if the Character Shadow and Decal options are ticked. Only untick Projectors if you really need a few extra fps.
Decals - Decals are the dynamic marks left on surfaces by weapons fire, explosions and the like. Tick this option to improve the realism of the game, but untick to gain more fps, especially on levels where there are lots of players firing lots of weapons.
Coronas - A corona is the glare given off from light sources, such as lamps and shock-combo explosions. Unticking this option will give you slightly more fps, especially if you also have Dynamic Lighting ticked.
Decal Stay - This setting, if the Decal option is ticked (and Projectors is also ticked), will determine how long decals (scorch marks and the like) will remain on surfaces. The three settings are Low, Normal and High, and unless you are a stickler for detail, Normal should be just fine. Setting it to High may negatively impact your fps slightly, especially with lots of players and weapons fire on screen.
Foliage - As the setting name suggests, ticking this option enables grass and other decorative foliage. Unticking it will improve your fps slightly on levels like DM-Antalus, but then again it makes the ground look very bare.
Trilinear - This makes the graphics and colors seem smoother and cleaner, but can reduce performance quite noticeable if you have an older (GeForce2) video card. Most newer systems should notice little if any performance drop from having this enabled. I've noticed that some systems will not start UT2003 or crash to desktop quickly with this setting enabled and everything set on the highest available. Untick it in that case, or lower some of your other settings slightly.
Use Blob Shadows - This makes the shadows (if Projectors is ticked) much less complex and hence easier for your system to draw. Tick this option to reduce shadow quality but gain a few fps on older machines.