I have an iPhone 3gs that I want to put music on?

But my itunes still has the stuff from my iTouch on it. And I don't know how to get rid of that so I can put music on my iphone. Any help would be appreciated!

Use iFunbox:
http://dl.i-funbox.com/

Get your mp3 files and just copy them to your iPhone using it quick tool box
hope it helps.