First-time home-buyers who buy between now and November could get either an $8K or 10%-of-home-value tax credit, whichever is lower. Remember: it's a dollar-for-dollar tax cut, not a liability reduction (which would only save you a paltry $1K).
So, let's math out the $8K part.
If you owe $8K in income taxes and qualify for the $8K tax credit, you owe nothing ($8K-$8K=0). I know what you're thinking, and the answer's yes... If you're liable for $3K in income tax, you'd instead get a check for $5K ($8K-$3K=$5K).