I've found similar problems and slow running on both win98 and xp which have reduced significantly after uninstalling adobe acrobat, winzip, and real player. My personal opinion is that they are all (somewhat) malware-laden, resource-hogging, cumbersome to use bloatware. A good, very lghtweight alternative to adobe acrobat is called foxit reader, it can be got here;
http://www.foxitsoftware.com/it's a stand-alone utility, just download to the desktop.
http://www.extractnow.com/ is for a winzip replacement-this one comes with an installer.I'm using real/quicktime alternative from file forum, its about an 8 mb download, though.Have you tried looking in the mouse settings under properties to see if it has a problem, updating or reinstalling the driver, or is that getting a bit freaky? Under mouse settings you could try lowering the speed a bit..not sure if that will help or not.
And of course in the stickys for this forum there are brilliant lists of software that may assist. The ones I've listed are true freeware,no ads etc.