Instructions
Download Liberty (see Resources). The team behind this emulator claims that it's able to play hundreds of Game Boy games. Another plus is that Liberty supports Palm OS devices that have color screens. Click the "Download" link to download the installation file.
Install GBulator (see Resources). GBulator not only supports classic Game Boy games, but can also play the newer Game Boy Color titles. You can obtain this software by clicking the "Download" link on the GBulator page.
Play Game Boy games on your Palm using Phoinix (see Resources). This emulator tends to play Game Boy games much closer to their original speed thanks to some tricks by the developers. However, you should back up the data on your Palm OS device because these tricks can be dangerous.