Try disabling Catalyst AI.

At the moment, I'm using ATI Catalyst driver version 6.2 for Window 98 SE. I think it's the last version that runs OK on Win9x. Inside the ATI control panel, I cannot see an option which says "Disable Catalyst AI". Inside the ATI control panel, I see these options -

3D settings -> Click on "Compatibility button" ->
Support DXT texture formats (Currently Enabled)
Alternate pixel center (Currently Disabled)

OpenGL Compatibility settings ->
Force Z-buffer depth = Disabled
Triple Buffering = Disabled

Options ->
Re-activate all warning messages (checkbox ticked)
Enabled ATI taskbar icon application (checkbox ticked)
Show ATI icon on taskbar (checkbox ticked)
Disable quick resolution feature (checkbox not ticked)
Also, 2 options about DVI...

Any ideas please? Thanks.

Not sure if this applies to these older cards, but with AA support Nvidia was always ahead.

And didn't the Voodoo cards have Supersampling AA?

I tried 2 more games - the retail versions of Unreal and Unreal Tournament. Both of these games do not show any visual improvement when I activate AA. I double-checked that Jedi Knight was working with AA, and it was. Perhaps the Radeon 9800's ability to successfully do AA in Windows 98 is limited. Maybe I need to use a more modern version of the Catalyst driver, and therefore use Windows XP? I'm a bit disappointed, because I wanted to get a few more games working with AA in Win98.

If you don't have Catalyst AI, can you just rename your EXE files to get around it?

Catalyst AI = Internal game profiles