I've just put an ATI Radeon HD 2600 Pro (AGP) into my desktop. Windows display settings don't detect a video card, dxdiag doesn't detect any video card, and even the AMD Catalyst Control Center doesn't display any video options.
I've installed the latest drivers (according to AMD/ATI). Their auto-detect software detected the card and said the drivers were up to date.
Obviously the card is "working" because the display is usable. However since the computer doesn't seem to detect anything about the card, none of the features are being used.
Here are my system specs:
AMD Athlon 64 dual core 4200+ 2.2 GHz
MSI K8N Neo2 Platinum 939 Motherboard
Windows 7 Home Premium, 32 bit (just did a clean install)