Update: I'm copying/pasting this directly from the Epocrates FAQ page:
Will Epocrates products work Palm's webOS devices such as the Pre and the Pixi?
Epocrates will be discontinuing support for Palm webOS devices. There will be one more update to the existing static, non-updating version. Should you need to install the product, please do so by 1 February 2011 at the latest.
The end of life for this version of Epocrates will be May 2011.
Here's how you can install Epocrates for Palm webOS.
1. Open your Launcher (the icon with the arrow) and select the App Catalog.
2. Within the App Catalog, do a search for Epocrates.
3. Tap on the line that displays Epocrates and then select Install to install the free App.
4. Once Epocrates has installed, tap on it to open the application.
5. Enter your Epocrates username and password.
6. Accept the License Agreement.
Your device must have webOS version 1.35 or higher to install Epocrates. Here's how you can find your webOS version.
1. Open the Launcher on your device.
2. Select Device Info (you might need to scroll sideways to find this icon).
3. Next "Version" will be the Palm webOS version number. If it is less than 1.35, please see your carrier for updates.
* Epocrates is not actively testing Palm webOS 2; these devices are not supported by Epocrates.
* Epocrates does not support the MotionApps Palm Classic Emulator.
* You have the option of continuing to use Epocrates on your Palm webOS device by going to online.epocrates.com. The site has been optimized for viewing on your device and contains Epocrates drug, disease and diagnostic information.
* We are not discontinuing support for all Palm devices; discontinued support applies to devices that use the Palm webOS operating system (e.g. Palm Pre and Palm Pixi).
* Palm "classic" OS remains fully supported.
* If you are in the market for a new device, we suggest looking into Epocrates products for other platforms such as iPhone and Android.