How do you run multiple JVMs on a single machine? How do you call methods in a different JVM?
This doens't make any sense.
It's easy to install different JVMs, just install the various JREs, JDKs, etc.
To execute the different one, you would use the proper java command from each install. Many projects rely on JAVA_HOME for this setting.
If you're talking about multiple JVMs in a browser for applets, I can't help you.