First, a clarification. The current tax break is a DEDUCTION not a credit. A deduction is when part of your income is shielded from being taxed. If you already paid tax on it, you get a refund. So for a $2000 deduction, you get maybe $300 in reduced tax.
A tax CREDIT is not shielding your income from tax, but rather the government 'paying' part of the tax for you. So a $2750 tax credit, you get $2750 reduction in your tax, assuming AMT doesn't kill it all for you.
Currently, for the 2005 tax year, the break is a deduction. It was supposed to be $1000 deduction but a tax bill applied last year suspended the phase-out of the deduction for 2004 and 2005 tax years, allowing the full $2000 deduction for hybrids.
As of 2006, the deduction has been replaced by a 'limited edition' tax credit for hybrids based on their efficiency. I say 'limited edition' because the credit ends after a certain period after a manufacturer sells 60,000 hybrids after the beginning of the 2006 tax year.
Both apply to new car purchases. The deduction doesn't apply to leases either, I am not so sure about the new credit, but I think leases are excluded there too.