I just got Amplitube metal, and I thought all I needed now was a guitar cable that is normal on one end but on the other end it is small enough to fit into my computer. (My friend has one) But said friend claims I need some kind of converter box. Is he right?
Yeah you need an audio interface google it, they come in all prices
^yup, you need one.
You could download AISO4all, then get an adapter thats 1/8"-1/4" for your cable if you want to spend as little as possible. It wont sound as good as an Interface but you could try it.
You don't need one, an adapter will do. Id you're happy with the sounds you're getting and use it a lot, a converter box (interface) is well worth the money.