Hi all,
My opinion is this.
Do not use Win98 or WinME on a machine that is connected to the internet for any period of time, i.e, connected via ADSL broadband or whatever. Dial up is better If you must, but then then do not use it to do any banking, buying or do not store any sensitive data on it. These operating systems are just not secure any more (if they ever were).
A virus that kills your hardware or wipes your data might seem nasty but there is much worse out there.
The machine will be enslaved as a bot sending viagra emails for the russian mafia and you will not know. It will harvest your contacts and logon passwords and thus weaken the defenses of your friends and favorite forums.
ClamAV is the defacto antivirus for Debian linux and Ubuntu users, there is a version that runs on most versions of windows including 98 and ME.
http://www.clamwin.com/
It is not one of those bloatware hogs that slows your PC to a crawl when you boot or start a program. But that means it is not fool proof. You must elect to scan a file or folder after you download it. It will not protect you from malicious script in websites. For that use a secure web browser,but I'm afraid I dont know if you can still get a version of Firefox or the like that runs on WinME.
If you want you and your friends to be safe from nasty stuff. Get a secure operating system straight away.
Ubuntu is great and completely free. You can set it up to dual boot your machine so you can keep WinME for playing your favorite Windows games. Use Ubuntu to safely browse the web and download what you like. Scan it for viruses and save it to a folder shared with windows then disconnect from the net and reboot to windows.