Hi,
I've already used the N709Q modem, but not the GPS one.I used different GPS modems, and the principle should be the same anyway;
If you let me see the schematics of your board and the code you already developed , i might be able to help you finish this in a couple of hours as i ve experience interfacing custom boards to Windows (all of them are video cards though).
Please see PMB for the real price and for more details.