You're not being clear here. Here's what I think you mean:
First, you can't use the iPaq as a BT adapter for your desktop. That's just not going to work.
Second, you can't share the desktop internet connection with a 7650 through an iPaq, AFAIK -- the iPaq doesn't have any connection sharing in that direction, and I don't think it can be used as a bridge. In fact, I'd be surprised if the 7650 supports any Internet connection not originated it.
Sorry
I'm pretty sure I'm right, but if you prove otherwise, by all means let us know.
--janak