Windows Mobile Professional devices sporting a widescreen will suffer incompatibility issues with some applications (like games running only on certain resolutions or navigation software), due to the extended resolutions these devices run on, let it be 480×800 (WVGA) or 240×400 (WQVGA).
XDA Developers launched WVGAFIX3, which is an application that allows you to change your screen resolution (yes, change, not emulate or tweak) on your device, running, according to the author, WM5.0, WM6.0, WM6.1 and WM6.5. You need to download this application from its home thread and extract the zip file containing two cabs and copy them to your device. First you will need to install SdkCerts.cab and then WVGAFIX3.cab (both go to Device), followed by a soft reset.
Launching the application will allow you to choose a custom resolution for display, which it will actually set, without stretching. As a consequence, applications that had incompatibility issues with native resolutions have increased chance of running, since from this moment your device is reported to sport and run a display with the resolution equal to the one you have just set.