I have also heard rumors of a 7300 on the Inquirer which I have posted on the forum. But it doesn't look all that fantastic at 4 pipelines, basically an overclocked 6200.
A cheap 8-pipeline 6600 - which is available in AGP today - would probably be better.
you're thinking of the 6800gs. the 7800gs along with the 7600 and 7200 are all cards that people have found referred to within the nvidia driver, so they may or may not actually be coming out in the future.