CEONSS

Some people may want to have a play around with this. It's the 64bit version of ut2004.exe.

Link

Personally I found it messes up some of the lighting in-game, but some people claim to have some benefits. As far as I know there's isn't any risk in trying it. Extract to your ut2004 folder and run the ut2004-win64.exe from your system folder. To use the original, run ut2004.exe.

I have tried it when i installed the gog version of ut2004, my experiences:
Pro:
-The game starts at least 3 times faster
Con:
-It messed up all vehicle sounds, meaning, when i get into one, the sound was like the engine is running at full power, even when i was idling
-TTS was not working.
so i'm not to fond of it

Playing already 64b on Ubuntu, no problem..

Just copying you're ut2004.ini and rename it to ut2004-win64.ini : it work