After speaking to a mac technician, upgrading to Leopard can be thwart with problems. He recommended:
1. Archive Install.
____ Else,
2. Back up all your files, reformat, clean install, then re-incorporate your personal files.
A simple upgrade from an earlier OSX to Leopard can result in internet browser & other problems. eg: unable to access your previous popular sites with your browser. And other issues.
This thread is simply intended as a consideration for those have or are intending to upgrade their OSX to Leopard, not as a hard & fast rule.
Chances are that if you follow the above advice, you will not have any problems running & connecting with LW.