Network works; Internet does not

Question

I apologize if this is a repost, I looked through everything and couldn't find anything exactly appropiate to me.
I connect on a university's LAN, no password or anything like that. All the network settings are basically "plug-and-play," if you will. Yesterday I came back to my dorm and found I simply could not get online. With most sudden changes like this, I usually suspect the ethernet cable, so I plugged it in again, checked for problems, replaced it, tried it in my roommate's jack (who's internet is functioning fine) and found that wasn't it.
So I moved on and checked my network settings. System Preferences said I was connected to the network and the internet, and a IP address was assigned to me. I left it for a while, and revisited it just now, and found no improvement. I disabled every NIC except for the ethernet controller, for good measure. However, I did notice that my shared music was showing up in my friend's iTunes. Then I logged on Bonjour, and found I could communicate with other Bonjour users. So, I am, in fact, connected to the network. Nobody else that I have talked too, even those running similar systems to me, is experiencing any problems.
So, instead of filing a complaint with ResLife, I decided that the problem must be on my end. But I cannot for the life imagine what it is. I have little experience with networking on Macs, and, so, I don't know where to start. Does anyone have any ideas?
Also, I don't have any types of security software, including internet security. I imagine the entire campus-wide network is behind a firewall, but my computer does not have an individual one.
Thanks in advance!
-Peter

Answer 1

Wow, thanks for all the responses!
Well, first I tried entering in those DNS servers. I tried them individually and together (and applied settings ), and there was no change.
The IP address the network's (hopefully) assigned me is: 141.164.95.xxx.
I've been careful not to turn on any proxies, although I don't completely understand the Mac's proxy set-up window. It's on the "Manual" set-up page, and I've made sure that none of the checkboxes have been checked (I have not altered them during the entire course of this incident, although I have, however, stared at them for great amounts of time, as I have stared at every screen in network preferences trying to figure out what isn't right).
I'm connecting using DHCP (no required usernames or passwords). One thing I did change was the search domain, AFTER this problem arose. When looking over the university's connection instructions, trying to figure out what may be wrong, I noticed that they said you should enter in the university's domain as the search domain, so I did. No PPoE is set-up, which is correct.
Another thing I tried was looking at the System Monitor to try to see if anything that's not supposed to be running is running (on the off chance I had downloaded some sort-of harmful program or something that cut off my access to the internet) and the list was fairly short, as I'm trying to keep all my applications closed during this diagnosis for simplicity. Everything seemed to be a system process or a widget.
I opened up the network monitor. I saw that I was recieving and sending packets. I verified this information by logging on somebody's shared music in iTunes, and rapidly changing songs, and the packet rates went up accordingly.
The Network Diagnostic tool refused to do anything; as it thinks I'm connected to a network and the internet. Apple should change it so it also pings apple.com or something; but that's just my two cents
And that's about it. I hope I'm not giving away a confusing amount of information, I'm just trying to walk everyone through what I've already tried (as insignificant to my problem as every one of my attempts probably are).