There are two ways that I have done it in the past with Win2k (yes they both use the same process)
1) Use Disk Cloning software to copy all the data from your smaller drive to your larger drive. Norton Ghost works great for this.
2) Start the install process for WinXP again but dont go throught the whole process! Simply stick your XP CD into the machine, tell the machine that you want to start a fresh install, and let it copy all the files to the HDD. Reboot the system. Once this happens it should have edited the boot record to give you three options now: Win Xp normal, Win98, and WinXP Install/Setup. Select the WinXP normal and boot into XP like usual. THEN, once in XP, go to your System Properties window (right click on My Computer and select Properties), select Advanced tab, then Startup and recovery button. Once in there select WinXP normal as your Default OS and click apply.
You might want to clean up the leftover install files that XP makes during the first part of this process but it does work.
Let me know if you need any more assistance.
OF COURSE, Ghost would be the easiest
