To Mosby: The River Cam is simply the river through Cam(bridge).

And if you're ever in Oxford, Mosby, the two rivers there are the Isis and Cherwell. For some reason, the Thames river is actually the Isis in Oxford. (Anyone know the story behind that?)

Is the Thames called the Isis at Oxford? I know that's what the guide books all say, but most people in Oxford actually call the Thames "the river" or "the Thames". Some members of the main university there call it the Isis, but mainly under very precise circumstances relating to rowing. The term now has a strong connotation of pseudery
Why the silly name at all? Well, there are of course lots of explanations - but no evidence the term was used before the 14th century (by which time the university, and the town, had been long established, and the river had been documented as the Thames for over a thousand years). It's almost certainly a pretentious invention by a writer who was trying to show off.
Which doubtless means someone will dig up a Roman inscription referring to the Isis next week.
And Cambridge is far too boring to have a controversy about what its river is really called. Take your trip to Oxford: it's a zillion times more fun.

any thoughts about best days to go to (or avoid) cambridge? i seem to remember the shops were all closed on sunday - or maybe we got downtown too late. anyone know what nights for evening song?

Having been several times to Oxbridge towns it's hard to recommend one over the other. Though not peas in a pod, each have there own calling. You can't go wrong.

To Terrb900: As elswhere in England, most shops in Cambridge are shut on Sundays, although this is beginning to change. For some people that might be a good reason to choose Sunday for a visit.

Terry: Evensong
The bad news: most Cambridge evensong happens only in term time. For detailed times at Kings (possibly the best in the world, for choir, architecture and ambience)go to the Kings College website. Other colleges (Trinity and Emmanuel, and maybe others) do evensong some days: Google on "evensong, Cambridge"