It won't be on the Sun Java site, it's an OS feature not a JVM feature. If it's
32bit Solaris I don't know what the maximum vm is that you can allocate to a
process, probably 4GB.

Besides the overriding OS limitation, there are also limits set by your system
administrator. These are defined by ulimit. You may need to modify ulimit for
the Tomcat process to allow it to allocate more virtual memory space. You can
test it from the command line by running:
$ java -Xmx2G -version
it will fail until you set the correct ulimit value.

E.g. on my system:
$ ulimit -S -v 2000000
$ java -Xmx2G -version
Error occurred during initialization of VM
Could not reserve enough space for object heap
Could not create the Java virtual machine.

$ ulimit -S -v 3000000
$ java -Xmx2G -version
java version "1.6.0_01"
...

To increase your ulimit above the hard limit you will need root access.

32-bit or 64-bit JVM?  Both seem to be available for SPARC/Solaris
systems.

Also, it has been a while since I have used Solaris regularly, but I
suppose it may still be possible to boot into a 32-bit kernel on that
OS and hardware.  If so, that would be worth checking.

  - Logan