Minecraft problems

[thewherewolf]

i am trying to play minecraft on minecraft.net, but i keep getting a black screen over the area of which the game screen would be,

ubuntu 11.4 and i've installed java icedtea package, sun java 6 jre and jdk, i don't know at all what to do,

also, i'm 15, so i'm looking for help that pretty much spells it out for me, thanks