I think trying it on another network is a good idea. You might also try using a USB wireless card if you have one just to see if it's the Mac's wifi. Also I didn't see if you tried, but disable dhcp and use a static ip.
Neither of those suggestions solves your problem but may send you down a different troubleshooting path.
Neither of those suggestions solves your problem but may send you down a different troubleshooting path.