I will be moving to the Palm Springs area at the end of this month (February).
To rent a bike, the guy to contact is the Bike Man (shop name) in Palm Desert. Kevin Brown is the owner and he can be reached at (760) 341-5022. I don't think he has a website, but I can send you his e-mail if you ping me back channel.
Lots of open places to ride out there. I like to get out and ride along Dillon Road. It runs parallel to the interstate, a couple of miles north of the interstate. Nice rolling hills, decent, but not great road surface. Go early, by mid day the winds are picking up. Dillon Road is about 35 miles long one way and you can easily do a loop on it and cut back down from the middle. If you don't mind getting in the car and driving 40 minutes, you can go to Borrego Springs and climb up the 12 mile long climb on Montezuma. Awesome climb as you are zig zagging up the side of a mountain, looking out over the desert on your left the whole way. On a clear day you can see forever. There is a great 50 mile loop that I like to do that starts with that climb.
For weather, its starting to warm up in March, expect an average high around 80 degrees and an average low around 50.
Mike Plumb, TriPower MultiSports
Professional Running, Cycling and Multisport Coaching, F.I.S.T. Certified
http://www.tripower.org