My father-in-law's computer did exactly the same. He had W98 and whatever version of IE that came with that (5.0.n.n.n).
I updated him to latest 6.0 plus SPs, did a Windows Update, did a Virus Scan (having got the latest definitions), scoured the Internet for other solutions and implemented them all (including changes to system.ini and Config.sys) and, after many many hours I gave up and installed Opera.
If you find the answer I would love to know it.
Timothy