Note: It seems that this software hasn’t been updated for several years – the version linked to this page is the latest to exist, so do not bother searching any further.
ATI Radeon XPRESS XPRESS 200/Radeon 1150/Radeon X1200/Radeon X1250 South Bridge Driver 10.2 is a driver that supports the Radeon:
It runs on Windows 2000 and XP. It is supplied with utilities to control compatibility.
You can download and use this product for free.