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.

See http://www.microsoft.com/windows/virtual-pc/download.aspx

Kees