Sure you can.
Change the hardware, then boot from the Windows CD, and use the 'repair' option.
You will need to re-activate Windows, but it should work with no problem.
I've done it a number of times, including motherboard upgrades.
I would definitely recommend a re-install but I have done what you are asking with 98 and ME [never XP]. I went into "device manager" and deleted the sound, video, many of the items under "system devices" and anything else that is specific to your old board. Leave the keyboard and mouse. Then shut down and move to new machine. Start the new machine. At start up Windows will start re-installing all the new devices and the ones you deleted. I had several duplicate entries under "system devices" when I was done but just deleted them and restarted again and all was fine. Good Luck