Migrate/Upgrade SBS 2003 to Exchange 2003 Enterprise

I have a client who is currently going through a growth phase. They have a SBS 2003 that will soon no longer support their Exchange needs. I see that MS has released a Transition pack to migrate from SBS 2003 R2 to Svr2003 and Exchange 2003. The question I have is will I need to first upgrade their SBS 2003 to R2 prior to running the transition pack?