Boot from EXT HDD from a cloned copy of Windows XP

To briefly explain my situation, I have a stripped down work desktop that runs Windows XP at my home. The desktop allows me to telecommute on days I don't need to be in the office. The machine has proprietary software and my work won't give me a laptop with the software, so my hope is to clone the desktop to an external hdd and boot from that hard drive on my Macbook.

Is this possible? I have read in other threads that to boot from an external hdd with XP you have to modify the install cd. But this isn't an option for me as I need my macbook to be able to act like a replica of my work desktop. Thanks for your help in advance.