Apologies for the double post, but the situation seems to have gotten even stranger.
MTA is still timing out when I try to connect to any server. If I then refresh the server list, it says it's scanned all the servers but found none, then after I quit MTA and open up firefox, every single web page I try to view times out. I can just log into the router from firefox and restart it then it will load web pages again. Very odd.
The router I'm using is a Belkin Wireless G Modem Router, and I'm hard-wired to it with an ethernet cable. Got the box for the router here and can't find any model name apart from Wireless G Modem Router...