[ziggytrix]

well, if you replaced the mobo with the exact same model you wouldn't need to reinstall your OS, but trying to run as OS that was installed on a different motherboard will be unstable at best.

you could also get a 2nd hard drive and install the new OS on it, keeping the 2nd HD as a slave drive, which would save you the trouble of backing up all your old papers, music, etc. this is assuming you have room in your case for another drive.