thankx squirrelmoose but it would more helpful if someone could give me step by step details.
to be very precise let me explain once again what do i want::

let suppose that i have created a domain (using DCPROMO) in windows 2003 server and made 4 user(using DSA.MSC) and i connected other 4 pcs which are having XP as OS to the domain now i want to allot certain space for each user lets say 2 GB for each user so that they can save their work on that drive and access it once they log on using their username and password.