As I now own a Magellan Maestro 4050, which unlike my 4250 has bluetooth and a headphone jack, I decided to upgrade the software. After hunting around a little I found Miopocket 4.0, a complete shell replacement for WinCE 4.x through 6.x GPS devices including smartphones with touch. It implements an iPhone-like interface and provides dozens of utilities, apps, and games.
At the Santa Cruz Flea Market I got, among other things, a Magellan Maestro 4050. I already have a slightly later unit, but this one has bluetooth. They run WinCE 5 which means most relevantly that they have persistent storage. WinCE 4 and earlier devices almost uniformly have only volatile memory, so when your battery runs out, your device resets itself to its factory settings. This was likely the best design decision Microsoft could have made, because WinCE 4 was an unreliable pile of debris that would corrupt its own installation at the slightest opportunity.
Let's say you have a GPS and you want to use it with multiple applications. On Linux, this is easy, because basically every program today utilizes GPSd for GPS communications. GPSd connects one or more clients to one or more GPS devices, and also has support for NTP (for providing time information.) However, it does not support Windows (and in fact they are fairly nasty about it) even though it's a fairly simple trick when using Cygwin.
After spending several hours looking, however, I did finally find a free (as in beer) solution that works for Windows XP. It involves the extremely hard-to-locate (but not any more!) gpsd from gps3d...
You might actually be looking for this other page from which I get occasional page referrals. It has ready-made binaries.
I purchased this unit from geeks.com, who had it on sale. While continually sold as a "generic" module, it's actually made by GoPass (a taiwanese hardware manufacturer.) GoPass also makes a handful of other neat GPS items, including some cheaper/lower-quality GPS units, and some GPS tracking units for cars that have GSM/SMS/GPRS functionality so you can ask them where they are.
This is, bar none, the best value in a Bluetooth GPS. It has support for WAAS and EGNOS, it has twenty channels, and it has an external antenna jack. The unit is tiny, smaller than my motorola flip phone, and it has a Li-Ion battery that the manufacturer claims gives ten hours of runtime.