I was in an accident last August where an idiot ran a red light doing about 35 mph and t-boned my car. For me, the pain didn't really develop for a day or two, so you may not yet be feeling the full effects. Definitely get yourself to a doctor and a physiotherapist that specializes in motor vehicle accident injuries. They can assess your range of motion and strength (and pain levels) and can give you stretches to do at first and then strength-building exercises to get you back to as near-normal as you can.
I recommend advil or aleve type meds for pain, and you may want to get a heating pad if you don't have one. Massage therapy will also be a big help. I'm of the opinion at this point (over six months later, and I'm still going to physiotherapy) that whiplash never goes away completely, but you will become much more aware of your posture and anatomy over the coming weeks
Don't worry so much about your car at this point - just make sure you take care of yourself first. The person who rear-ended you should be paying for everything, and as others have mentioned, don't sign anything that says you're fine and don't need any treatment until a year or two has passed and you really are back to normal.
Good luck, and I hope you and your friend recover well.