It is easy to think that developing an application for Windows Mobile using the built in GPS unit requires a lot and complex code. Luckily this is not the case. You can actually have the base for a .NET Compact Framework GPS application up and running in less than 10 minutes if you choose the correct tools.
This post describes what I have found to be the easiest and fastest way to create an application that is interacting with the GPS unit in .NET Compact Framework.
Windows Mobile have created a sample for using the GPS intermediate driver from managed code and this is all you need to get started. The sample is included with the Windows Mobile 6 Professional SDK. How to use this is explained very well at the Windows Mobile Development Center: Using the GPS Intermediate Driver from Managed Code.
If you do not have any special needs you can use this directly by compiling the sample and adding the .dll as a reference in your project. If you need to customize it you can simply just add the sample source code to your project and modify/extend it where needed.