from Iphone 3G to Iphone 3Gs

Hey

got the upgrade via new contract at ATT. So my iTunes was/is used to my Iphone 3G. Now I want to put my music on my new Iphone 3Gs - but iTunes seems not to do it. It shows a message asking my to "erase and sync" - anybody knows if that applies only for the music library or will it affect the apps and the new features of the 3Gs?
Thanks for any input

cheers

i believe that "erase and sync" is just apple terminology for;
erase the music etc from the iphone 3Gs ( but there is nothing on it so little will happen)
AND
sync all the apps, music etc from in itunes (the ones on the iphone 3G)