Rabies pointed this out to me. According to some forumers (one said they tried it and it worked) you can do this to get Doom 3 to run in Windows 98.Open up Doom3.exe with a hex editor.
Do a search for 'GlobalMemoryStatusEx'.
Change the '45 78' corresponding to 'Ex' with '00 00'"
Close the hex editor.
Run Doom3.exe
Try at your own risk!