The Quest supports 800x480, but NOT 480x800... which is why you have to rotate to landscape before starting it. The 800x480 resolution mode was programed in for some HP PPC which didn't have a portrait mode.
Here's another fun trick: You can download the iphone version of the quest from this site, and use that main quest database with your windows mobile version. It gives you a couple bug fixes, and 2 or 3 new quests and a couple new areas to explore. I think the iphone version is 5.0 GOLD or something like that. Its been a few months since I did all this. Basically, download it from the iphone section, and open the apple container file that you download. I believe I was able to just use a current version of winrar to open it. Once inside, you will find both an updated main quest database, and an updated expansion pack database. Copy those two files over your existing ones on your windows mobile phone, and your all set. You don't need any other files. I've tested this and it works 100 percent. I've played all the new content, with zero problems. Enjoy the new areas.
If anyone has problems with this, I could be swayed to write up step by step instructions.