There is 2 methods:
just bung the new hd in the system and hope windows figures it all out. I have done this before, and it worked sometimes. Other times the windows install would kinda freak out and BSOD.
There is a proper method, which involves somethign along the lines of opening device manager, removing all system devices, then next time you reboot the hd in the new system it will reinstall the correct things for your new system.
There are many pitfalls, and as some have said. It's oftern best with windows just to do a reinstall.