Getting PocketPC audio to play on truck's speakers

[sanddrag]

I sometimes use my PocketPC and bluetooth GPS receiver to give me directions while I'm driving. The problem is though I don't like having to take my eyes off the road to look at the screen, and the road noise in my truck is so loud that I can hardly hear the directions that is gives out over the tiny little built in speaker. And I don't want to drive with an earpiece. So, I want it to play the directions on my truck's factory audio system.

I've seen those things that you plug into the headphone jack that broadcast a radio signal and that seems like a pretty good solution for the price but there's another problem with that. I'd have to change radio stations to hear it. I like listening to the radio while I drive, and I don't really want to have to switch stations to hear the GPS because I might be on my music station while the GPS is saying something important on its own station.

So, what I need to be able to do is have the PocketPC interrupt whatever is playing on the truck's factory audio system, and "speak" the directions, then resume whatever I was listening to when it is done "speaking"

Is there any possible way to do this? It is a Dell Axim X30 PocketPC with integrated bluetooth running Windows Mobile 2003 and it is a 1999 Ford ranger xlt with the "premium" factory audio system.

Thanks.

EDIT: To answer the below question: it is the Navteq gps system.