| Well basically with an OEM copy of windows you can replace anything but the mobo. Once you replace the mobo it counts as a new system and so you are required to buy a new license. With a retail copy you'll just transfer you're license over to the new system. When you activate you're copy of windows a hardware profile or something is sent to microsoft as an ID for your system but I'm not sure if they check these things or whether calling them and saying it's the same system will work.
__________________ 19" Dell Ultrasharp 1907FP l Rosewill RT550-135-SL 550w | Abit AN8 32x l AMD 64 X2 3800+ @2.6Ghz | Rosewill RCX-Z3 cpu cooler PNY 8800GTS 320MB @580/1800 | Maxtor 40GB, Seagate 160GB l 2GB PC3200 OCZ Platinum XTC   |