So, quick guide from me, you might want to try this. What is Mouse Acceleration: Don't confuse this with mouse speed, which is basically how fast your pointer moves. What Mouse Acceleration does is, if you move your (physical) mouse from X to Y and you do this fast, your pointer moves further than if you move the mouse slowly. On Win XP this is called "Enhanced Pointer Precission". Many players find this bad, because it makes it harder to get a feel for where your pointer will end up after a mouse movement.
This setting is on by default, so you might give it a try turned off. I have it off for a week now, and I have the feeling that it might be more effective for me this way.
So what you do is the following:
1. Go to Control Panel, Mouse. On the "Pointer Options" Tab, turn "Enhanced Pointer Precission" off.
2. Run regedit and navigate to HKEY_CURRENT_USER\Control Panel\Mouse. Use File->Export->Selected Branch to backup your mouse settings, in case you want to undo Step 3
3. Get mouse_fix.zip, extract it and doubleclick the .reg file (open it with notepad first if you are feeling paranoid).
That should turn off all mouse manipulating effects in Win XP - you can still change your mouse speed in the Pointer Options, but your pointer movement should now be in a direct relation to your mouse movement.
If you want to undo step 3, just doubleclick the .reg file you exported in step 2.