...how would I do it?
I suggest Amazon.
I havn't used it yet but I am about too =] It's very trustworthy and I have used it a lot to buy things. Just bought my ipod nano new =]
Go on amazon.co.uk - Your in England right? - and there should be a tab saying 'sell your stuff'. You will have to make an account and everything.
Good luck =]
ebay is the site to sell stuff..you dont need a card to sell stuff.
do you need a credit or debit card to sell things?