<p>I've seen a few fixes for allowing PNG images to have transparency in Internet Explorer 6, but I've yet to find one that also allows you to set the background position in CSS. If you use sprites, it's a deal-breaker. I've resorted to using GIF's (which are not as high quality), not using transparent images at all, or serving a completely different stylesheet to IE6. Is there a fix for IE6 that allows for PNG transparencies AND background positioning?</p>

Yes.  Convert your images to use indexed pallets (png256).  You can support transparency (just like gif), but not an alpha channel.
You can do this using
Irfanview
and the pngout plugin,
pngquant
or
pngnq
.
The YUI performance team also did a
great presentation
that covers this an many other image optimization concepts.