I don't think I would have been running Doom3 on less than normal settings, Farcry runs over 40fps with everything except AA on highest, and it don't bitch about 98!
You are at your limit of memory that you can use with Windows 98 - you'd eventually have to upgrade because
Windows 98 isn't designed to handle more the 1GB of RAM.
"It's not the years, it's the mileage" ~Indiana Jones
Vic Fontaine for President