You're doing your employer a great service with this, too bad it can't be put into $$$$ value easily.
Regarding the Windows AGP HD2xxx driver, AFAIK there never was an issue like the one we're seeing with Linux fglrx now,
I could get 7-10, 7-11 and 7-12 working with Windows by force-installing them, it's just that an INF file in the installer did not include all chipset IDs so that when setup.exe was launched, it wouldn't recognise a supported (or at least working chipset) card in the system.
Sapphire had/has a knowledge base articel on their website on how to modify that INF and H.I.S. has a self-modified version of the Catalyst 7-10 bundle on their website that I suspect will work with all HD2xxx AGP cards.
If I'm correct then the update to the 8-1 driver for AGP was a DirectX fix on an issue that got introduced with the ordinary Catalyst 8-1 release?
I guess what I'm trying to say is that I would be positively surprised if looking into the Windows situation would provide much help for the Linux fglrx issues with the HD2xxx card.
Despite (relatively minor) installation issues the Windows XP drivers have been working with these cards pretty okay all the time since their release in September, at least as far as Catalyst 7-x (x=9 to 12) are concerned.