How come I could not copy & paste to iTUnes 9.0?

[fiberwalker]

As I have 2 PCs, I also have 2 version of iTunes. One is lastest which is installed to my newest rig running Win7 while older version of iTunes 9.0 is installed onto my old rig running Win XP Pro. I have this query which I hope that someone can assist. I have several attempts in trying to copy & paste as usual what I did with my iTunes 10.5 on my Win 7 which is not allowing me to successfully copy & paste my music to be sync with my iPhone. How come it's only viable with my iPhone 4 on my new rig with iTunes 10.5 but not enabling me to do so with my older version iTune 9.0 and Win XP Pro? Thank you.