Here's a guide I wrote for setting up Unreal Tournament: Game of the Year Edition on modern PCs.

1. Download and install the latest Oldunreal patch.

2. Download and install Unreal Tournament Bonus Pack #4.

3. When starting up UT99 set the renderer to OpenGL if you're on Nvidia or Direct 3D 9 if you're on AMD, then launch the game.

4. In the game open Options, then Preferences, then go to the Video tab and set the FPS limit to 100 to avoid gameplay issues.

5. Go to the Network tab and set the Internet Connection to LAN.

6. Go to the Input tab, disable mouse smoothing and select Raw Input for the best possible mouse input.

7. To Increase system memory go to <path-to-game>\System\ and edit "UnrealTournament.ini". Find the line "CacheSizeMegs", set it to higher values like 64 or 128.

8. To change the FOV go to <path-to-game>\System\ and edit "User.ini". Find "DesiredFOV" and "DefaultFOV" and set the values to whatever you want. I use 106 on my 16:9 monitor.

NOTE: Anti-Aliasing and Anisotropic Filtering can be enabled in the renderer settings. Open the console by pressing ~, type "preferences", and hit enter. Click on the Rendering tab and select the renderer you are using. The values for MaxAnisotropy and NumAASamples can be from 0 to 16. Make sure to set UseAA to True to enable Anti-Aliasing.

There are four UT Bouns Packs in total and they are not cumulative. So, forgive my ignorance but why do you recommend to install just the #4 alone? Are other three included inside GOTY edition of the game or with an unofficial patch? And why not to replace renderers with the updated unofficial versions as well, which wold support modern video hardware?

The first 3 packs are bundled in with the GOTY edition. The unofficial patch does include the updated versions of Chris Dohnal's renderers. On a side note, I did try enabling AA in Direct 3D 9, but it doesn't seem to work.

After following the directions in the OP, when I change the resolution from 640x480 to anything bigger the game turns into a smaller window with some of the screen cut off in the window.

How do I get sound? I tried all the audio settings.

Are you sure it's actually being pointed to a valid audio output and not just the first port it saw?

I tried all options.