Thanks for the clear explanation kRayner - it's always a big help to see such a well structured post
Windows 7 should have chipset drivers for the i945 already, so I'd be surprised if that caused the symptoms you've experienced on that particular laptop (although I've installed them ok using Vista compatibility mode). Did you do a clean install of Windows RC?
When you mentioned scrolling seems to lag, it could be that you need to update your ATI X1600 drivers. When I've used a graphics card that Vista didn't recognise out of the box it sometimes caused this jerky scroll issue until I installed new drivers and restarted the PC.
It's worth trying anyway, as there are proper Windows 7 drivers for most ATI cards now:
http://support.amd.com/us/gpudownload/Pages/index.aspx