If you don't mind taking a bit of a risk, you could try getting a copy of Windows 98 from somewhere like eBay - A quick search revealed a fair few original CD's knocking around for only a few quid.

I've not come across much that SpyBot can't permenantly remove, but you'd probably save yourself a lot of hassle in the long run by getting hold of a cheap copy of Windows 98, reformatting and starting from scratch.

I'm not a particular fan of Windows 98 but if it does what you want and ain't broke, then why fix it I guess.