I usually try to read forums from users to see what issues they are experiencing with their systems. Recently I came upon this issue from a few users after upgrading to Apple’s Snow Leopard OS:
After upgrading to Snow Leopard from 10.5.8, a few MacBook Pro models would consistently drop their connection whether it was via Ethernet (wired) or through AirPort (wired and wireless are using DHCP). Several supposed fixes suggested on the web offered limited success:
* Reset Network settings, delete "Automatic" settings and created a new setting (called untitled)
* Zap the PRAM (hold Command+Option+P+R on restart)
* Flush the DNS cache
These 'fixes' seemed to work for only for a few minutes, and the connection would eventually drop again. NOTE: Although other computers and drives would be visible on the network, and Instant Messaging via Adium is still functional, users could not connect to the web through a browser.
Users who contacted Apple Support were advised to try the following steps:
* Shutdown the MacBook Pro and remove the battery. Then disconnect the power, and then hold the Power Key for 15 seconds. Afterwards replace the battery, reconnect power and zap PRAM and wait for 2 chimes before letting the keys go.
Connections were restored, but only for a short time.
Another suggestion from Apple Support:
* Trash the System Configuration folder and all contents... then reboot.
The above suggestion seemed logical because it would remove any existing preferences that may be corrupted and affecting the connection setup. The system would then recreate a fresh preference file free of any lingering old settings. This worked for a short time, but then again both wired and wireless connections would drop within a few minutes of usage. It is also worth noting that simply restarting the MacBook Pro regains connectivity as well but drops after a few minutes on both Ethernet and Airport settings.
Please keep these thoughts and suggested fixes in mind when upgrading to Snow Leopard (10.6) on the MacBook Pro. I would hope that Apple is aware of these issues and is working to resolve them.