Every program ever will try to use your CPU to the fullest extent. It is completely healthy and normal to see a process use 100% (on a single core, or 50% on a dual-core usually). Why not go to the Crysis forums and complain about C++? Your problem is that your processor is not just barely under the minimum, but very far under the minimum requirements, not that Java is inefficient or slow. Not only that, your processor is severely bottlenecking your video card, and ATi drivers are notorious for having poor OpenGL support.
It's your computer, not Java. For the record, I'm using Ubuntu 10.10 with an Intel integrated chipset that doesn't have OpenGL 2.0 support, 1.5GB of memory, and a dual core processor clocking about 1.8Ghz, and the game regularly gets about 20-30fps - just as much as WoW on here.
Edit: Sorry if this sounds stand-offish. I'm a huge advocate of Java programs and this kind of hit me the wrong way. My recommendation would be to pick up a cheap dual core if possible; that would dramatically improve your performance in virtually everything, especially on Vista, 7 and Linux.
Have you tried updating/re-installing Java as per the Technical Help Sticky? The Java will use nearly all the CPU time on an older single core CPU. A lower speed rated dual core is almost better for running this game.
There also seems to be something odd going on with some users using ATI X1000 series cards and the final driver release for them.