That's one of the questions i have too. Also haven't been able to find an answer yet. If you're really interested in getting a PMP you might want to look into the ARCHOS AV 700 or possibly the PMA 400 or 500.
I have a quicky review on the various PMPs that are available
here. It's just based on the information available online as I haven't gotten a chance to play with any of them yet. If you're willing to spend the money, I think ARCHOS' offerings are amazingly good. I especially like how they have built-in DVR capabilities and how the PMAs are linux-powered and have PIM and internet functionality as well.