Your hard drive will work, but you will have to buy a new OS. The windows operating system on Dell's are OEM, They are tied to the system they came on, so Microsoft will not allow you to register it on a new system.
Also, Dell adds tons of crap that only works with Dell systems.
But if you go to Newegg.com you can get a OEM copy of windows xp for $99.
It is never a good idea to use a windows installation from a previous system anyways. Any time you change out a motherboard, you need to do a fresh install of your OS. That's because the chipset drivers from the old motherboard can cause problems with the chipset from the new motherboard. And it is not easy to just delete the old chipset drivers, if not right out impossible.
