FIRST this is probably in the wrong place. my apologies

so: after hours of pain i have finally managed to get linux mint 10 to function WITH INTERNET on my laptop.
so i thought i'd play a nice java game (minecraft obviously) and go to bed. but no.

how are you supposed to run a .jar? i have tried all sorts of things and all i end up with is a glowing coffee bean symbol and a task bar entry saying java that vanishes after 20 seconds.

does anyone know how to run a jar file in KDE?

please help a noob in distress