I don't know of any free ones other than Clamwin.
http://www.clamwin.com/Clamwin doesn't do real time scanning. You have to manually scan or schedule it to scan in order to look for viruses. That may be an advantage for a gaming computer because it won't conflict with running a game. But it's not as secure as a real time scanner that can catch things before they get on your computer.
There may be others, but I'm not familiar with any.
Clamwin is based on clamav, which has been used as an antivirus for computers using Linux for years. Even though Linux might be unaffected by most viruses, Linux users didn't want to pass them on to Windows computers so clamav was developed.
Be very careful where you browse in Windows 98 and be sure to disable VBscript.
http://www.sophos.com/support/knowledgebase/article/10359.html Unless you do programming, you'll never use it. But there are viruses that use it to infect.
You can also remove or rename the wscript.exe file in C:\Windows
You can catch viruses just by browsing to a particular website. Even a trusted wesite can be hacked and have malicious scripting added.
To secure your web browser, you might try installing an older version of Firefox (version 2) and then try to get the NoScript addon for it. That will block most malicious attempts to hijack your computer through your web browser just by browsing.