1) If your phone is rooted - use ShootMe application.
ShootMe allows you to take screenshots of your device.
Just fire up ShootMe and give a good sustained shake or shout to take a screenshot.
If present, the light sensor can be used as well.
Use MENU to toggle the trigger/mode.
Only supports ROOTED devices.
2) If your phone is not rooted (if you have not rooted your phone, then follow this):
a) Install the Android SDK on your PC. Link: http://developer.android.com/sdk/index.html
b) Enable USB debugging on your phone (Settings>Apps>Development)
c) Run DDMS from the tools directory in PC
d) Select your phone from the list, Menu > Device > Screen capture.