|Is there an error message during the install process? What do you mean with this?|
"I have tried an XP Pro cd (just to see if it would boot from it (no go)
It was telling me no disc was found, till I took the HDD out, popped it into one of my external cases and reformatted it in there... now, I just get a dashing little white line"
Were you expecting a desktop with the XP CD? Reformatting externally is not needed since the install process will format and prep the drive.
Do you have the recovery disks for the system? Setting the BIOS to default can cause install problems on systems that are designed for Vista. Some have a setting for AHCI mode that prevents an XP intall. In order to continue the hard drive access needs to be set to IDE or compatibility mode to continue the install. Using the recovery disk for XP gets around that problem since it bypasses the AHCI problem.