Did you read through the following?
Getting Your GapiDraw 3.8 Application to Compile With GapiDraw 4
The GapiDraw build for WM5 is for Windows Mobile 5.0 and later, including Windows Mobile 6.0, 6.1 and 6.5 (we have several not-yet-released WM 6.5 devices in house that we test against regularly). The WM 5.0 build does not use GAPI but instead uses the AllKeys API and DirectDraw for blitting to the screen, and is required to use if you are building for the Windows Marketplace.
I also recommend that you read through the following:
GapiDraw Versions (WM 5.0 and PPC 2003)
If you still have questions after reading through the readme - add me on Skype (jsanneblad) and I'll help you out so you're up and running in no time!