I'm having similar problems with my 1.83 GHz MacBook Pro 15" Core Duo: I have excellent wifi signal strength on my second, later gen MacBook Pro and an HP Laptop on the same wireless router, but the first gen MacBook Pro signal strength constantly fluctuates from strong to none regardless of where it's positioned. It looks like a pain, but I'm tempted to replace the antenna.

The antenna cable connectors are seated to the card properly, and the visible cable up to the monitor appears intact, so I'm wondering if the portion inside the monitor is broken? Can anyone provide positive feedback regarding antenna replacement vs. replacing just the card?