Getting music from another itunes account

Hello,

I just got an iphone4 and this is my first time using itunes for anything...i set up my account and synced my phone to the itunes account but i do not have any music...my friend has had her itunes account for a while and she has a ton of music...i would like to get the music from her itunes account onto my iphone and i was told that i was able to do that but i can not figure out how to do it...and also i want to know if i plug my iphone into her computer will all of my stuff sync to her computer bc i do not want that to happen i want my computer to remain the computer where i sync all of my information...all i want is her music

Thank you soooo much i would really appreciate it if someone could help me with this!!! :)