I have a Dell 537s Vista 64 bit Home Premium O/S installed and was upgrading to the Win 7 64 bit Home Premium.
I tried Dell again with great results. It was as simple as loading the Win 7 O/S disk first, letting it start up then removing it.Then, putting the Dell "Assistant" disk back in, letting it load, then removing it. Then putting the Win 7 O/S disk in again to complete load. It took about an hour +/- and works perfectly now! Best of luck to anyone else who has this problem. Fortunately for me, a simple fix.