There doesn't seem to be an easy way like on the iPhone (pressing both buttons at the same time) to take a screen shot on Android devices - however if you've got the Android SDK installed it's pretty easy.

1. Connect your device to your computer via USB
2. On the device (Android 2.1) go to Settings > Applications > Development and enable 'USB Debugging'
3. In your Android SDK folder run the DDMS app in the tools folder
4. From the left panel select your device and press CTRL + S
5. Now find the screen you want to screen shot and click 'Refresh' and then save the image.