I just set up a new computer with an MSI 870 -G45 and a Radeon HD 5850 (detailed specs below), on Windows XP 32-Bit. Everything went fairly smoothly, I installed the graphics drivers that came on the DVD and everything seemed fine. Then I went and updated the Catalyst drives, and the next time I rebooted I was in 640x480x4bit color. When I try to start the CCC I get the error "currently active gpu is not supported". I'm unable to change the screen resolution at all even in the windows settings. I un-installed the new drivers and grabbed the MSI drivers for 870 -G45 from the website and that fixed it. Unfortunately those drivers (from early 2010...) don't support OpenCL. I also tried some older Radeon drivers (10.10) from the ATI website and had the same problem.
Note: There is nothing wrong with the Radeon 5850, it's been removed from a perfectly functioning PC.
MSI 870 -G45
Radeon HD 5850 (In PCI_E2 slot)
Phenom 2 X4 810
OCZ 1000W Power Supply
Kingston Value Ram 4 GB
Windows XP 32-Bit