No, he's saying x64 doesn't exist. The 64bit x86 CPUs are called AMD64 and EM64T (or 80686, 686, i686).

Anyway, the launcher and the DLLs are compiled in 32bit and that's probably why LimeWire is running in 32bit mode. They make up only 1% (if not less) of the total code base and there's nothing in the native code that would benefit from 64bit!

The remaining 99% are pure Java byte code that run on the top of the JVM and LimeWire as a Java application would inherit the 64bit features. (Un)fortunately makes LimeWire very rarely use of 64bit arithmetic (long, double) so that you'd notice no difference.

The JVM may benefit from the substantial number of CPU registers but the original design of the JVM is a Stack Machine that has no registers at all. I dunno if Sun manages to benefit from it.