It seems illogical but this sort of question normally gets answered in the "hardware section", but there perhaps there should be an OS section. See if  this discussion is helpful.

Most likely problem is using the "wrong" SDK ie non Sun/Oracle, despite the fact that processing comes with its own SDK. If you've got  a 64 bit distro then running opengl is a problem that is dealt with separately.

yes, other people seem to have the same problems (but i don't when i tried it)

http://forum.processing.org/topic/can-t-run-processing-in-ubuntu-10-04lts-64-bit

http://forum.processing.org/topic/ubuntu-is-logging-me-out-when-i-m-trying-to-run-program-in-processing

my suspicion is that opengl sketches and compiz don't get on, so try turning off 3d desktop effects.

plus what monkstone said about java, you want the proper Sun (Oracle?) Java packages.

plus video card / video card drivers. ATI support is traditionally not as good as nvidia support. although that may've changed since i last looked.

I'm running 1.2.1 on two 32-bit Lucid-powered machines with nVidia graphics chipsets. With some exceptions things are working well. I'm using JDK 1.6, btw. I don't have Compiz or any other desktop effects on either machine.

Best,

dp