What will happen is, once you join the OCR team, a new profile will be created with your name, and you can then switch back and forth between teams if you want, but only the team you specified in the program will get the Work Unit credit. But yeah, you can join multiple teams.
Even if you are on dialup, the only time you need an internet connection is when you're recieving the data package to be processed, or when you're sending to processed data back to stanford. Usually those pieces of data aren't larger than 5 megs.