optical drive is the rom drive (cd, dvd, cd-rw, DVD-rw)
I'm not too sure about your bios as HP usually have a proprietry bios.
You say when you unhook the extra drive the pc won't boot but are you sure you're unhooking the correct drive??
This is really quite perplexing because as I stated earlier unhooking the extra drive shouldn't alter the boot drive.
The graphics card won't be the problem.
This is worrying me
no matter which grive i try to install to it says inspecting system as usual starts loading drivers then stops on the normal blue screen and says windows has been shut down to protect the system etc
You don't usually get this error message unless windows is try to load, can you describe your methodology for installing XP please.