The only fully supported ATI cards under the standard x.org driver that will work pretty much straight out of the box is for anything in the 9250 range and older, anything higher like the 9800 or and of the X and HD series requires the utterly horrible ATI binary blob driver, ATI nad now since they've been bought by AMD have again stated that they'd like to source their drivers, which would bennifit them and us equally, they'd finally have drivers that worked as advertised for Linux, Windows and OS X and we'd finally be able to get things working as advertised.
No it's not about geting paid money to support or not support, the graphics cards get a great many updates to their design instruction sets, your 9000 Pro is only an R200 series card, it only supports OpenGL 1.4 and DirectX 8.1 instructionsets natively in card, DX games have to have a dumbed down engine to run while OGL can force things to run, but through software tricks which are much slower then having it in card. look here
http://en.wikipedia.org/wiki/Radeon_R200
If all else fails grab a new card, anything from nvidia's 7300GT line and up work great of AGP, tho anything past the 7600GT is a little overkill for little gain over the 7600GT unless you find it on a good sale, save for the hackjob cards that aren't officially supported for AGP slots like the XFX mod 7950GT, it uses custom windows only drivers cause it's not officially supported by nvidia.
but the line goes like this from weakest to fastest, 7300GT, 7600GS, 7600GT, 7800GS, 7900GT. Overclocked cards are a waste of cash unless they are either the same price as the stock ones or unless they come with a good 3rd party cooling system, something quite a bit more beefy then the stock cooler so long as the price isn't higher then getting the card and buying the cooler your self.
All 7x00 series cards support OpenGL 2.0 and DirectX 9.0c and all will smoke your 9000 Pro in any game you throw at them.
Tho I haven't heard anything about any 8x00 seores cards being released for AGP those cards will support OpenGL 3.0 when it's released next year and already support DirectX 10, only if yo run vista tho, if you run XP tho they still run DX9 games just fine.