Hmm, the problem you have sounds quite strange. It sounds like there is something wrong with the mouse internally. Have you tried cleaning the laser thing on the bottom of your mouse? It might be that there is something stuck there which causes your mouse to freak out.
Apart from that, the different speed movements really sounds like something that is caused by software or mouse incompatibility, since you only have it with games.
EDIT: Have you also tried to use the mouse on another surface? Some mouses are unable to function correctly on one surface but work very well on another.
Assuming it happens in numerous games and only games, perhaps there is a setting within the trust software which causes this to happen?
Apart from that, try to see if you have the same problem with the mouse on another computer (Well the different speeds in games) without installing any drivers that you gain with the CD.
If none of this helps anything I will assume that the mouse you bought doesn't work well and you should perhaps return it to the shop where you got it from and tell them your problem and that you wish to have a new one.