SBS 2003 and Transistion Pack

Currently we have SBS 2003 Prem.. we only have 2 users left (75 user limit) I want to upgrade my SBS 2003 to a stand alone Windows 2003. I spoke with Microsoft Licensing Dept. and they told me that I have to buy a transition pack and then CALs that way I can upgrade my SBS 2003 to a stand alone. My question is: How hard is the upgrading procedure… when I do a upgrade using the transition pack.. would my files/folders/user directories/Active directory settings would remain the same.. or everything will be gone/deleted and I have to start from scratch just like installing 2003 server on a new machine… Please help me out… Thanks in Advance!!!