ipod classic on mac and PC?

Hey,
I just bought a new ipod classic. I loaded it up with everything on itunes on my Macbook, and now i'm at my friends house and want to get the music from her PC. It says i have to restore the ipod (deleting everything obviously) for windows to recognize it.

Does that mean i cant use it on a mac and a pc? That can't make sense? My sister has an ipod classic and it works on both.
It's cool if i just need to restore it once, but i want to make sure if i do my macbook won't say the same thing next time i connect it.

Any help would be greatly appreciated!

Thanks

Discussion of illegal activity (such as pirating music) is prohibited by our Forum Rules. Please review them and refrain from such discussion in the future.