Server: Potential serious problems: Domain controllers or BDC's, dynamic disks (or software RAID). A clean install really is the best option. Old NT CD-RW drivers can do bad things to W2k as well.

Workstation: Ditto on CD-RW drivers. Back up first if you want to try it.

Overall, I think Tony's right. My only thought is that you make a SP4 slipstreamed install CD before you start (or whatever SP you want to go to). Good info here.

-Zeke