I have a ATI Radeon 9600 Pro (Atlantis) card. In my constant battle for better framerates I tweaked and renamed and what have you, but I only accidently stumbled across the tab in DirectX-3D-settings where you set your AGP speed (simple didnīt think of taking a look there because I would not have dreamed about anything being wrong there...): surprise! AGP speed was set to "off"!! I turned it to 4x, because my system is able to handle that. Catalyst/SmartGuard self-tested stability after required re-boot, and: second surprise! AGP was "off" again!!!
I browsed various internet boards and found out that 100s of ATI users had exactly that problem, and 10s of well-meant suggestions wouldnīt work! AGP was simply not recognized, although BIOS settings etc. had AGP shown and enabled. Many users noticed that problem after having upgraded to the latest Catalyst drivers (4.1 or 4.2; it was 4.1 in my case).
Only ONE solution worked (at least for me): AFTER upgrading to the latest Catalyst driver you should also update your chipset drivers, which in my case is a VIA chipset. Their latest drivers include an AGP patch. Got the VIA 4in1 driver (from here: http://www.viaarena.com/?PageID=2 ), installed, went to my AGP settings - and: surprise! AGP speed now enabled and correctly set to "4x"!
Ok., fellow ATI users: Do check your AGP speed settings in your DirectX-3D tabs. (Obviously, many people would not check there because they simple assume that their system surely has AGP enabled!). If you find it "off", and have a VIA chipset, install their latest drivers!
Oh, I forgot: yes, fps went up (slightly....).