Prepaid cards aren't really "credit" cards, because they aren't extending any credit to you at all. You give the card company your own money, and they usually deduct several types of fees from the funds that you give them. Your "credit" limit will be however much is left of your own money once they're done with it. It seriously sucks.
You can probably get a "secured" credit card, which works in much the same way as prepaid, but the one BIG plus is that most of those companies will report to the credit bureaus and that can help to raise your FICO score.
People typically use secured cards to establish or re-establish their credit, and then they move on to better things. If you do go with a secured card, make absolutely certain that they will report to the credit bureaus, otherwise you are just wasting money.
After suffering from poor credit ratings for a while, my first decent credit card was through Wamu (formerly Washington Mutual) and they gave me an initial line of $2000 with a 0% interest rate for the first six months. That helped me to consolidate my crappy cards and get them paid off before the interest started accumulating.
Hope that helps and good luck!
BTW, Capital One may issue you a card, but they are known for not reporting your limit to the bureaus, which can actually lower your score. The reason for this is that 30% of your score is based on what percentage of your available credit has been spent, and if there is no reported limit on a card, FICO will assume that whatever your greatest reported balance has been IS the limit on that card. Therefore, if you have a $1000 limit, but you've only put $100 on that card - well, you are only at 10% of what you have but the score will assume that you are at 100% and that will significantly lower your score.
(Sorry I can't explain it better) I've heard that Capital One plans to start reporting limits, but until that actually happens I would try to avoid them - especially since you already have a not so great score to begin with.