Some students have reported problems getting onto IRC and specifically into #seneca. The reason for this is that we have changed the channel's mode such that only registered users (i.e., nicks) can join. This was done to stop an endless barrage of spambots from joining and leaving the channel.
It turns out that registering your nick is a smart thing to do, as it means people can't steal your identity. You only need to register your nick once, and then your IRC client will auto-identify you on the server each time you join.
I've added a question on the FAQ under IRC (see #7) that gives you info on how to do this. If you're still having trouble, talk to someone down in ORI at one of the Mozilla workstations.