JBoss products are 100% pure Java, and will run on 32 or 64 bit hardware with a compliant JVM.
Benefits of 64-bit JVM on 64-bit OS & Hardware:
Wider datapath : the pipe between RAM & CPU is doubled, improves performance of memory-bound applications
64-bit memory addressing gives virtually unlimited (1 exabyte) heap allocation (note, large heaps affect garbage collection)
Issues with 32-bit JVM on 64-bit OS & Hardware:
On Linux x86_64, the JDK1.3 requires a work around to run. See Linux64andJDK1.3
Applications which run with more than 1.5GB of RAM (including free space for garbage collection optimization) should utilize the 64-bit JVM. Generally speaking, applications which run on 32-bit virtual machines which do not require more than minimal heap sizes will gain nothing from a 64-bit JVM and will likely require more memory to run the same code (the 64 bit addresses among other issues). Barring memory issues, 64-bit hardware with the same relative clock speed and architecture will not likely run Java applications faster than their 32-bit cousin. Because many server applications require a great deal of memory, 64-bit hardware should be considered for new purchases.