I understand your frustation, but Nvidia does this as well. I have a Dell notebook that uses a Nvidia chipset that suffers the same problem you are having.
The issue with AMD/ATI is not new and is not going to change. XP is an obsolete OS, by many regards, and continuing to write drivers for older systems doesn't make financial sense for AMD/ATI.
AMD/ATI supports Vista and Win 7 because; 1) it is the same driver, and 2) is what is being sold today.
What Radeon Mobility GPU are you trying to update the drivers for - and- on what notebook (make/model)?