Hi there,
You can try out Pocket GBA found here:
SUNBUG, For Mobile Things the install is a CAB file. Activesync your device to your computer. In the Activesync window click Explore and then cut and paste the CAB file onto your device, either it's main memory or the SD card. Use File Explorer on the device and simply click the CAB file to install. You can place the ROM files in the same way. Don't know how good the key mapping will be, but you can let us know that after you have tried it out!