Turning old HD into a bootable HD for a Dell??

I just upgraded the HD in my 2006 MBP from a 120 GB to a 640 GB. The old hard drive is currently sitting in an enclosure gathering dust.

I have an old Dell Inspiron laptop I bought in 2003 that I am using at work. The computer is so worn out that it has difficulty doing two things at once (literally).

I got to thinking...could I reformat the old 120 GB HD to work with windows, install XP on it, and use it as an external bootable hard drive for the old Dell? I don't have the Dell in front of me right now, so I can't check the BIOS to see if USB booting is even possible.

Anyway...I was just wondering if this is even something that is possible, and if so would it help the performance of the computer?

Well my Dell Latitude has had problems doing one thing at once from new lol! USB booting is possible after formatting and partitioning, however have read XP will not install on an external drive. You may have to pop it in and install that way.

Wonder if the 120GB drive would make the Dell work faster, particularly if it is a 7200RPM drive?