Satcomer
In Geostationary Orbit
I have read among the Apple Discussions and found a fix for a 10.5.x Mac not speaking to a D-link wireless router. If you go into the wireless D-Link router (that was working before a 10.5.x upgrade) and drop the fragmentation threshold and the frame threshold to 2306. This might fix your problem.
Also disabling IPv6 (in System Preferences->Network->Airport and turn of IPv6) might help.
Also disabling IPv6 (in System Preferences->Network->Airport and turn of IPv6) might help.