Following are the steps to check your Windows XP / Vista's Activation Status :
Windows XP :
Goto Start Menu and Select Run
Type oobe/msoobe /a and press Enter
There will be a dialog window will appear and let you know the activation status.
Windows Vista:
Goto Start Menu and Select Run
Type slmgr.vbs -dli and press Enter
There will be a dialog window will appear and let you know the activation status.