I was trying for more than a month to find a solution on how to get a Radeon 9800XT working with 3D acceleration enabled. The problem is that the current drivers (3.2.8 and 3.7.0) don't properly recognice the XT model while the PRO model works fine.
In case you have an XT then this is for you. If you have a PRO then you can also follow this but you don't need the additional steps.
First, you should follow the installation instructions in this thread.
If you don't have a Suse distribution then the information there should be also helpfull because the principal is the same on different distributions, only the tools are slightly different. I tried the above with a Suse 8.0 Pro and 8.2 Pro and it also worked fine. Then I switched to gentoo and the information still applies. Of course on gentoo the natural way (emerge ati-drivers) is much easier.
OK. After you have done everything as written in the thread above you have your driver installed but you can't run anything that uses OpenGL. You can verify this when you try to start KDE it will fail with an errormessage about DCOP KUniqueApplication.
If you do an lsmod afterwards you can see that agpgart has a usagecount (on my system it was always 2) and fglrx has none. If you run another windowmanager like fvwm2 and do an lsmod then you can see that fglrx is actually used because the usagecount increased. this means that your driver is basically working, but when your try to run glxgears (i.e. in fvwm2) it will quite with an error (SIGBUS or something).
If you have a PRO then your system should already be working. Now comes the additional step:
After you created the XF86Config-4 file with the fglxconfig you must load the XF86Config(-4) into an editor and add
Into the device section.
If you have multiple device sections then look for the one where this line is contained:
and write it right below. The actual position doesn' t matter as long as it is in the same device section.
Of course you have to do this when you are in the console with X exited.
This line simply tells the driver that you have a Radeon 9800PRO Chip installed. Since the PRO and XT are quite similar this works fine.
If you have questions or problems with this then you can contact me. I'm not used to writing tutorials or similar stuff, so everything is clear to me and works for me, but that doesn't mean that it is clear to you as well. Of course adding that one line should be sufficiently easy, so I really don't expect any problems with this.