The dropshadow is subtle, so you really should be able to do it with jpgs anyway.
Here’s the thing; it can be done with pngs, and there is a java script that will make pngs display properly in IE6 – but you can’t make that hack work with bg images.
Try this: cut your jpgs right to the edge of the shadow and try it out, see how it looks. You might be surprised how much you’re over thinking this. If you still can’t get the result you’re looking for, post your raw PSD file on your server and I’ll give you a hand w/ it.