You're misinterpreting the tax rebate. It is an advance on next year's refund, but with lower taxes next year.
As an example, if you paid $5,000 in taxes on your 2007 income, and make the same amount in 2008 (and the same deductions, etc) you will only be responsible for $4,400 of taxes in 2008. You are gettign taht $600 now, instead of next year. If your refund was $1,000 this year it wil be $1,000 next year, PLUS the $600 you get now. It's not like your refund will only be $400 next year because of the check.
Make sense?