how do I transfer contacts etc from iPhone 3g to iTunes for new iPhone 4gs

help.
how or what do i do to transfer my infomation including contacts from my old i-phone 3g, to the computer (i-tunes) and then save them for transfer to new 4gs:no:

First you will have to Sync your iPhone 3g contact to the iTunes and then allow it to sync contacts and then disconnect iPhone 3g and then connect iphone 4gs and then again sync contacts to the phone, if you want then you can also use MobileMe or say "cloud" service in order to sync the contacts. Hope that helps.