Do you have any unusual drivers on that machine? You could compare with some of the other machines. If you find any, disable or deinstall them and attempt the conversion again.
The usual suspect with BSODs is the disk controller, but your bug check id 50, not 7B, besides it BSODs after displaying the login screen. But, to be on the safe side, check you preselect LSI Logic for W2K3.
HTH
Plamen
