Hi Mei,
It seems very easy to install jBPM BPEL.
First you should download jboss-4.2.3.GA and extract it in a directory, download apache-ant and config ant correctly(mostly the ANT_HOME=xxxx,PATH=%PATH%;%ANT_HOME%/bin).
Second, you can modify config/build.properties, change software.installation.dir=${user.home} to your jboss directory.
Then you can enter deploy directory in bpel, and execute "ant main" to deploy jbpm-bpel.
enter examples/hello directory, and execute "ant main" to deploy hello example to jbpm-bpel.
execute "ant test" run a test, verify the hello example.
If you want to try other examples, you should install jswdp first. I are not familiar about that, So you have to try it by yourself.
regards.