I'm posting this just to database it, seeing as it was a bogus fix that wasn't answered anywhere in 3, 100 result pages of google search returns.

Some guy was talking about mouse lag with his cordless mouse(but had a high frame-rate) on the official UT forums to I decided to chime in(but fixed my own problem):

I am having a the same problem, but under slightly different conditions.

Were it a cordless mouse, the input lag would make a load of sense, but seeing that I am using one WITH a cord, I am confused. I had googled the problem, saw that it could *possibly* be sound related, which was believable; I was getting the problems when I upgraded to Vista. I tried every in-game(and out) audio option, with the same results.

So to recap:
- Corded trackball(I know, scoff if you want)
- High frame-rate
- Fine on XP -> Bogus on Vista
- Possible relation to audio
- Probable ID:10[t] error.

Any ideas? :P

EDIT: Fixed by doing something that I THOUGHT would do the exact opposite. I *unchecked* the 'Reduce Mouse Lag' option in the Input tab under settings in-game. And it's perfect now. Which, logically, seems to make absolutely no sense to me whatsoever.

So just in-case... here is an illogical fix: uncheck 'Reduce Mouse Lag'