OpenESB only comes with a number of useful ServiceEngines pre-installed when you get the NetBeans 6 download with the SOA pack. Say you want to install OpenESB separately. You might do this because you 1) want clustering and 2) have a headless environment and 3) don't want an IDE on the target box or 4) blah blah blah.
You may be surpised to discover that the only two components that are pre-installed with OpenESB 2 are the sun-http-binding and the sun-javaee-engine. If you want to execute a BPEL, you'll need that engine.
To see what you have installed, open the GlassFish console and point to JBI > Components and they'll all be listed there.
If you need to get more components, such as the BPEL engine, you can get them from here:
Scroll down to the section called OpenESB Component Downloads. This link lists the service engines and binding components you need. Download your item and drop it in the
And it will install automatically.