Unable to connect wireless connection via Mac Notebook

I recently purchased a Dell Inspiron 531 with the Vista Operating System.
Prior to this purchase, I was running an old Dell PC with a Wireless Router
connected (LikySys). My wife uses a Mac Notebook, which she was able to
connect to the internet via the wireless router. Since hooking up my new
Dell with Vista, my wife is unable to connect to the internet on her
Notebook. In addition, when she tries to connect, it will not only NOT allow
her access, it will kick the hard connected Dell off the internet as well.
The only way to re-connect to the internet with the Dell is to restart, and
turn off and on the wireless router as well as the modem. I have called
LinkSys, who have updated Firmware, so I am all set there. I called Dell,
and they are unable to help me. As a side note, I also have Norton Antivirus
running, which could possibly be an issue as well (although I have NOrton on
the last Dell and had no issues). Please help!!
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jrdiluigi