Help with ports

I am creating a program that will connect two users computers together and, at the moment, allows them to send messages between each other. I'm currently using TCP and port 8008. This works fine for people who have port 8008 open on their firewalls, but I have some friends who cannot do that. Is there a way to get this to work without needing a port opened? Is there a port always open (I thougt port 80 maybe) or can it be done using a different method (like UDP but that surely has same problem).
Thanks
Matt

I dont know a great deal about this subject. Although recently I purchased a book that deals with the subject briefly, so...

here is a list of port numbers I found, it aint complete but its friendly on the eye :-)

http://www.webopedia.com/quick_ref/portnumbers.asp

if you look at port 194 (Internet Relay Chat) I'd probably try this. According to this book Ive got: all ports below 1024 are 'privilaged ports' these are reserved for well known servies. But if 'person x' firewall is set to block port '194' their still gonna be doomed.

the difference between tcp and udp:

tcp: a connection based protocol with full handshaking, error detection and correction. To provide a reliable delivery service.

udp: described as a 'unreliable connectionless protocol'. It has no handshaking nor does it have error detection and correction.

Hope this info helps!

It does, thanks a lot and I have now got it working through firewalls.