What port number will HttpWebRequest use locally?

[Nick]

Is there a way to avoid using a specific TCP port number, on the client
side, when using HttpWebRequest?

I've written an HTTP server and client that can't communicate with each
other when the TCP port for the client is 1723 (which happens to be PPTP).
The XP SP2 firewall on the HTTP server computer (XP Pro)blocks the inbound
connection, even though the target TCP port is 80. Adding "exceptions" for
TCP/UDP port 1723 in the firewall makes no difference (I would think that
these are for local/listening port numbers anyhow). Shutting off the
firewall allows the connection through, but that's not a great solution.

When using WebRequest.Create(uri) to create a new HttpWebRequest object, the
client TCP port is provided automatically and loops (by default) from 1024
through 5000. When it gets to 1723, my client is blocked. Is there any way
to know which TCP port is being used locally by HttpWebRequest?

Thanks...