I got it sorted out. Thanks for all the replies.
Just so any other dc7100 owner knows, when you get a new graphics card for the pci-express slot and your computer doesnt recognise it, you have to push F10 on the start up to take you into the bios setup, then look through the menu until you find 'Hyperthreading' and change from enable to disable.
Then click save changes and exit, you will then need to plug your monitor into the new vid card and it will start up
This proves that we are not limited to HP's crappy little 64mb pci cards.
Only then will it allow you to install the drivers.
Thanks all for your help