Is it a subsidy?

I read about the new tax credit for plug-in hybrids that was passed by the U.S. Senate. From reading the summary about the credit it appears that it seems to favor the Chevy Volt. There has also been some discussions about extending loans or other financing to GM. This talk has been overshadowed by the Wall St. bail out but it is still in discussion. Does this new tax credit effectively subsidize GM and the Volt? Does it matter?