Ok, a few words on sensitivity issue =)
It's really individual but there are a few things to keep in mind when trying to set it for yourself.
As a rule of thumb your aim generally becomes better with lower sensitivity but you can't turn around fast enough when your sensitivity is really low. So, players who like to engage in close quarter combat tend to use higher sensitivity compared to those who like to keep their distance
Basically players toy with sensitivity trying to keep it fairly low but not to the point when it takes too long to turn around. It doesn't sound all that great but there's a way around this problem. The name of this way is "mouse acceleration".
When mouse acceleration is enabled faster mouse movement lead to higher sensitivity. It means that you can turn around swiftly when you move your mouse fast enough but you can keep you precise aim with not so fast mouse movement. It takes some time to get used to it and some people (me, for example) don't use it at all but as far as I know lots of really good UT players use this feature.
To enable mouse acceleration in UT you have to set it in windows (if you use default windows mouse drivers) control panel -> mouse. It is located right next to windows mouse sensitivity setting and takes form of checkbox in WinXP and slider in Win2000. After that you have to toy with "direct input" checkbox in UT. It goes this way: you change it, restart UT and look if anything have changed. If not, you change it again and restart UT one more time. Probably it will lead to desired result
If you use external mouse drivers like logitech setpoint software you need to set mouse acceleration somwhere inside this software but you won't have to deal with "direct input" checkbox in UT as far as I remember