i was on worm net a few hours ago and my opponent had created his gravestone how do you do this i want to know?

You can create your own in an art program and save it to *WWP's directory*\User\Graves. Make sure your grave is 24x32 in size and is a 256-colour BMP.

http://worms2d.info/Custom_team_grave

whenever i try to select that grave it exits the game :(

Try modelling it off one already there (ie opening one already there in paint and modifying it, using save as obviously instead of save). That makes sure all the settings are correct.