What version of AS/400 are you running?
This may work for you:
1. Start the Q shell
STRQSH
2. "cd" to the directory containing jt400.jar, e.g., something like:
cd "/QIBM/ProdData/HTTP/Public/jt400/lib"
3. Set the CLASSPATH environment variable and add jt400.jar
export CLASSPATH=./jt400.jar
4. Execute the AboutToolbox class:
java utilities.AboutToolbox
If your AS/400 is too old though, the AboutToolbox class doesn't exit. If this is the case, let me know.