You can't access a pool or connection outside of its own vm.
change your mind and write calls to session beans in jboss
set up a micro-jboss with only naming and pools (and maybe the tx manager) and run your other app inside it, say starting it with an mbean. (Then you could extend this to be the "application client" stuff ;-))
start the jboss pooling code "by hand" in your other app -- this is not really very hard, you just create the mbean in code and set its properties, then call start or startService.
Use someone elses pool. Choices may include Tyrex (apparently used in catalina) and poolman.
Unless you do (1), you will need xa drivers and (at least) Tyrex to get non jboss and in-jboss work into the same transaction.
The best option here (for me) is to write some EJB code. Not a problem. I just wanted to make sure.