General consensus is that the device doesnt have enough memory for minecraft. See the forums - this has been discussed there.
I never got Java working either, but I am pretty sure that was an issue with me, not Java!
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed. Here's an example...
"My grief counseller just died, luckily, he was so good, I didn't care."