iPhone Iphone/Itunes help Perlease!!

Hopefully someone can help!? going mad here!

Purchased 2 Ipod touches today for wee girl and the mrs both no probs to add songs to (drag to music folder in itunes and off you go)

then got to my iphone 3gs seems to only allow me to add music by going to add folder in the file menu in Itunes i.e wont allow me to drag music manually from multiple locations any ideas where im going wrong here!??

i think you may need to authorize your computer with the iphone your using..

go to itunes... click on store and then authorize computer

or use dtunes