I have the Navigon 40 Easy, which I believe is based around the same platform as yours. I've been able to get into Windows CE by replacing the PM.exe on the devices flash memory in the Navigon directory (back everything up first! The Navigon Fresh software is very useful for this)
I used System Information 1.6.1 and a basic menu with a couple of apps on it (GSfinder for example). I was able to launch IGO 8, however the issue lies with the detection of the GPS. I understand these later Navigon devices (from reading a German forum via google translate) that programs like IGO etc can not directly access the serial port. I certianly couldn't when I tried. I think there is a way, whereby you launch another program that runs in the background which allows you to access the serial port. However this is as far as I got.... I'm still trying however WindowsCE certainly isn't my area of expertise.
Massive apologies for not replying earlier. I used system information 1.6.1 renamed to PM.exe on the internal memory of the Navigon. I had created a previous menu system for an old sat nav that had a link to Gsfinder and control panel. Still haven't got any further though as I got side tracked a little. If you need anymore help let me know, I can send you my menu/ System information if you require.
The Navigon back up program (fresh I think) seems very good. I seriously messed the device up and it still managed to revive it