What kind of network is it? Do you get a logon prompt? Can you access files on the network? Did the laptop ever have an IP on this network, or is this the first time you tried to get it one? Was it not connected to the network for an extended time recently (like over the holidays)? Perhaps you lost your IP lease...
Go to someone else's PC that you confirmed has working IP --preferably the closest person to where your network jack is located, as it's a good bet that he/she is on the same segment. Note his/her DNS servers, gateway, subnet mask, and IP; from his/her computer, ping some IPs above and below until you find one that doesn't respond (timed out). Go back to your laptop and manually assign the IP, DNS, GW, SM. Restart and pray.
Also, you can try to bring your laptop to a the "good IP" place, plug it in and see what happens.
Note: Even if it works, this is just a temporary fix. Maybe the IP that didn't respond was previously being used by a computer, printer, etc. that happened to be off/disconnected, so snagging its IP will create a conflict (the first one to boot up will get the IP/internet). You should see a little popup box if/when that happens. Ideally, you should contact the network admin to have him help you with the IP problem...
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