From Paulo Taylor:
PalmMSN follows the MSN Messenger protocol from Microsoft meaning that now you can use your Palm to communicate with your MSN Buddies whenever you want. Basic functionality is implemented so that you can send and receive messages to any MSN client compliant with Microsoft MSN Messenger protocol. The features: add and delete contacts; change your screen name and status; insert time stamps in your messages; play sounds as messages arrive; block contacts; ability to keep connection alive; send and receive Typing events. PalmMSN was developed in Java so that other Java enabled devices like mobile phones can also use it.
Version 0.14 features unspecified improvements and bug fixes.
OS 5 (often called Garnet) includes a OS 1-4 emulator on it so it can run OS 3.5 programs. That isn't the issue. I have a feeling that you need Java on your Palm to make this work. Since it was written in Java, a Java Virtual Machine is needed to run it. There is one available on the Palm website in the Support Downloads section (the Tungsten E page has a link to the version for all supported devices). This is a moot point since the program no longer works.