Steve Jobs said 'before the end of 2003', so September - December 2003 is the release window.
From the beta builds' readmes, the requirements are exactly the same as for Jaguar. Practically no feature of Panther needs more oomph from your machine, instead, Panther will make it (feel) faster.
So: Your iMac DV will run Panther just fine, you can be sure of that. However, you might want to consider buying a new Mac, anyway, sometime next year, and that will have Panther preinstalled. So why shell out 129$, if you're going to buy a new iMac in March 2004? ;-)