misskitty, I hate to say it, but here goes: you are in serious trouble, and there's no way you're getting out of it without spending either some time, money, or probably both.
Let's start with the first issue, which is something that everyone with broadband should know: it is a horribly bad idea to plug in a broadband connection directly to your PC. You should get yourself a router, for several reasons. It's also not that expensive, so that's not an excuse:
- if you ever decide to share your connection with other PCs in your house, it'll make the job much easier, particularly if it's a wireless router.
- a router is essentially a perfect firewall. It makes you very secure from certain kinds of threats on the Internet.
misskitty, it sounds like what's happened to you is your computer has had some bad malware put on it. If you go out on the Internet, without a firewall on a broadband connection, make no mistake: you will get hit with malware. (This is the kind of attack that a router will stop cold.) Once you get hit with malware, strange and funny things happen: your case is not all that unusual.
The usual response to a system as thoroughly infested as yours is to back up all your data then reformat your system. However, with a system as old as yours it may not be possible or practical. You may or may not have your Windows CD available. Even if you have it, you may have to download security updates manually (since I don't think 98 has Windows Update).
If it's old enough to have 98, that system is at least six years old. I hate to say it, but it could be time for a new PC. Could someone fix your PC? Sure, but it would take even someone with a reasonable amount of PC knowledge the better part of a day, maybe more.
The other possible problem is that it's not malware, but the hardware of your PC itself is broken. With something that old, I can't rule that out, either.
Either way, it really sounds like it's time for a new computer. Having your broadband provider check if the whole installation was done right wouldn't hurt, but if he says it works, well... it's time to go PC shopping.