Yeah, I thought you meant permanent 0%. Come to think of it, I think AMEX is 0% on some of their cards as you pay off in full. They charge an annual fee though.
They're charge cards, so not really 0% but I know what you mean.
He doesn't use his card at all apart from the guitar. He's pretty much given the account to me. I have an additional card, so I do actually have a 0% card till June next year and an APR of 17.9% after that, but it doesn't help my own credit record does it.
No. As everyone has said, just make a couple of purchases per month on a card and make sure they're paid off. Over time, it will help you. But it will take time.