How to repay first time homebuyers credit

I'm wondering about the First Time HomeBuyers Credit for 2008. I know that I have to pay back the $7500 within a 15 year period of $500 per year. I know that you don't repay until after 2 years the home was bought. But how does it get paid?
Does it get paid by doing your taxes at the beginning of the year? Or do I send a check?
Can I pay more than $500 per year if I wanted to? If so, How??

Thank You