Process / Workflow in Java

I have a specific project that I need to undertake, and I would like to receive some instructions from the masters before I take the first step.

We have several applications that receive input from some external sources (for example, a file, XML-RPC, web service, etc.), then somehow process it, applying rules to it, exchanging data with others external systems (possibly), access to the database (possibly), and then sending a response. We support different versions of the same application to satisfy all the small differences between our customers. (Yes, yes, I know. It's terrible, so I want to fix it ...)

The idea I'm playing with is to have a component architecture where various components can connect through configuration and the flow of information is determined by business rules. This, in essence, should give each client a copy of the program with a different set of settings. I even dream of a GUI based application where the system can be connected together in a drag and drop style in the VB style.

So, the above sounds definitely like something that has been done before ... and I don't want to reinvent the wheel. The problem is that the above should be able to process large volumes of transactions in real time, so I'm not sure if the right BPEL is the right one.

Any recommendations before I go and make the wheel rounder?