xbox 360 connection problem

[#1]

I have an xbox 360 connected through plusnet.  I can sign into my Xbox live membership no problem but when i search for a game it takes about 5 minutes to connect to one.
I cant make a party or join a friends party.  I cant even do a private 1 on 1 chat, but I can send messages.  Can anyone help me on this situation as its driving me crazy, although the misses is loving it. 

[#2]

Sound like a firewall issue, Try putting the xbox In the DMZ.

[#3]

What is the DMZ and how do I do that?

[#4]

Try this port forwarding rather than DMZ  http://support.microsoft.com/kb/908874/en-us