Don't unerstand your problem.
Are you suggesting XP is beyond repair in the 120Gb disk?
You are saying with another 80Gb disk, with an operating system inside, you can see the 120Gb disk mounted.
Normally you can resize a XP partition and install Linux. In your case if XP doesn't work there is no way to know if a resizing exercise works or damages your XP. If the 120Gb disk is going down to install another 100 OS into it will not bring it back.
What you need is an opinion from another operating system on the "health" of the XP disk. This you can do by running a Linux Live CD and look at the output of the terminal command
If the hard disk has a healthy partition table then no error would be reported.
Also most Live CD has Grub inside and so you can activate a Grub shell and get the opinion from the horse's mouth by command
until the disks exhausted.