Yes, you can add that drive easily. And no, you can't boot from it and run XP.
The thing to do:
1. Do an 'anytime upgrade' to Windows 7 Pro or Ultimate.
2. Download the virtual XP that run under it.
3. Install your XP-only programs in that virtual OS.
I just purchased a new Dell 9100 desk top with windows 7 home premium. I want to add my old Dell Dimension 8300 hard drive with XP SP3 Home as a second drive. My main reason is I have some software that is not compatible with Win 7 and there are no updates available. Is this possible and how would I do this? Thanks in advance for any help.