1) Roaming profiles changed significantly from 2000/XP to Vista/win7. The Windows 7 machines will *not* pull down old roaming profiles saved by XP/2000 machines. You will need to use a tool such as the Windows Easy Transfer or USMT to trasnfer your usres'settings.
2) You didn't mention *which* weekend you planned on doing this rollout, so if you have some time to plan ahead, I'd go over and work through the documentation and use the tools here:
http://technet.microsoft.com/en-us/solutionaccelerators/dd407791.aspx
The deployment toolkit will let you automate the USMT process for migrating settings, will let you create a "master" image with all of the software you want installed prior to deployment, and covers that SID issue. But to get everything working right does require a bit of a learning curve, planning, and most importantly testing. I wouldn't want to go into a weekend set up without knowing what to expect.
As I said, there is some up-front invenstment in time in setting this up, but once done, you can deploy current and future machines all with the same process, so there is some long-term reward, even in an SBS environment. I recommend this process for any organization of decent size (10 workstations or more, give or take) due to the long term savings and consistent and predictable image deployment.