Everyone has given great advice here. Ann for the most part I agree with you. There are different things that need to be done. Yes, get your friend to a doctor and get them checked out. Next, report it to the law enforcement agency that has jurisdiction at the location the rape took place. Be there for your friend, make sure he or she has someone to talk to. And yeah, don't force your friend to talk, they will when they are ready.
There are some counceling centers that can help with this, and some special shelters that have programs to help him or her, which the law enforcement agency should give them information on. Ann made a good point, depending on the gender of your friend, asking for a male or female officer is good for comfort levels. This will deeply affect him or her, so don't expect them to just return to normal right away, it will take a lot of time, and talking. Reporting the crime, and the counceling, will allow your friend some closure to the situation.
Letting them know they didn't cause or deserve it is important. I know most of this is repeat information, but having dealt with plenty of rape victims myself, repeating is sometimes important. If you have any more questions or anything, feel free to send me an e-mail, I will help as much as I can. Take care
Pawz