I get "Inaccessable Boot Device" error after installing
new driver. Unable to start in safe mode, or any other
mode. I have installed XP along side to try and solve
the driver issue, but not sure what to do can anyone help?

This happens most of the time when you set wrong DMA mode for the newly installed drive (because you have mentioned that you installed a new drive.). It could be that you are using a 40 conductor cable instead of new 80 conductor cable. This depends on the motherboard you use. So try installing a new cable if you use the old one. Or visit Seagate.com and try troubleshooting they have provided more information on this. Read windows help for the error massage you get it too have some information.
Hope you’ll find the solution.
Oshadha.