I hope someone here can help me as ive been trying to sort this problem for ages without success :(

I play Enemy territory (Q3 engine) and my problem is that the "feeling" of the sensitivity changes, it can even change during gameplay!... sometimes it gets lower but most times its very fast / unstable and it makes it impossible to track propperly, it doesent matter how low or high i put the sens, its still very unstable/sluggish, note that no numbers change only the "feeling", (the cm's needed for a 360 turn are still the same) im not the only guy who are having these problems, we are a few guys trying to sort this but we havent had any success so far im afraid.

Ive tried everything i can think off, ive bought new mice... format, etc but this problem always reoccur, first i thought it was a strict USB problem... however its the same with Ps/2 aswell. ive tried every possible mousefix / DPI configuration... mouse drivers on and off... i simply cannot understand why the mouse act so weird