The flag -XXaltjvm doesn't work on amd64.
It should work the same way it does for sparcv9.

titanium2% cp /java/re/jdk/1.6.0/promoted/all/b30/binaries/solaris-amd64/fastdebug/jre/lib/amd64/server/libjvm.so ./
titanium2% setenv JAVA_HOME /java/re/jdk/1.6.0/promoted/all/b30/binaries/solaris-amd64
titanium2% /java/re/jdk/1.6.0/promoted/all/b30/binaries/solaris-amd64/bin/java -d64 -XXaltjvm=./ -version
There was an error trying to initialize the HPI library.
Please check your installation, HotSpot does not work correctly
when installed in the JDK 1.2 Solaris Production Release, or
with any JDK 1.1.x release.
Could not create the Java virtual machine.

###@###.### 2005-04-07 20:49:38 GMT