Move to SBS2003R2 from 2003 STD Domain

Wondering if someone can point me to the right info on best way to move from a 2003 STD domain to SBS 2003R2.

The existing DC is setup already, and we need to make the SBS the PDC. The existing 2003 DC will ideally become the backup DC on the network.

Note that the existing users are very picky about their desktop profiles, and we need to preserve them at all costs.