python reverse proxy spawning via cgi
You don't need to spawn another process, that would complicate things a lot. Here's how I would do it based on something similar in my current project : 

Create a WSGI application, which can live behind a web server.
Create a request handler (or "view") that is accessible from any URL mapping as long as the user doesn't have a session ID cookie.
In the request handler, the user can choose the target application and with it, the hostname, port number, etc. This request handler creates a connection to the target application, for example using httplib and assigns a session ID to it. It sets the session ID cookie and redirects the user back to the same page.
Now when your user hits the application, you can use the already open http connection to redirect the query. Note that WSGI supports passing back an open file-like object as response, including those provided by httplib, for increased performance.
I need to write a cgi page which will act like a reverse proxy between the user and another page (mbean).  The issue is that each mbean uses different port and I do not know ahead of time which port user will want to hit.
Therefore want I need to do is following:
A) Give user a page which will allow him to choose which application he wants to hit
B) spawn a reverse proxy base on information above (which gives me port, server, etc..)
C) the user connects to the remote mbean page via the reverse proxy and therefore never "leaves" the original page.
The reason for C is that user does not have direct access to any of the internal apps only has access to initial port 80.
I looked at twisted and it appears to me like it can do the job.  What I don't know is how to spawn twisted process from within cgi so that it can establish the connection and keep further connection within the reverse proxy framework.
BTW I am not married to twisted, if there is another tool that would do the job better, I am all ears.  I can't do things like mod_proxy (for instance) since the wide range of ports would make configuration rather silly (at around 1000 different proxy settings).