I have a panasonci hd video camera what cable do i need to hook up to my iMac desktop

It looks like a standard mini USB cable would work. It looks like this:

It depends on what Mac you have and what version of iMovie. You may need to use Firewire.

iMovie 11 - cameras supported:

http://help.apple.com/imovie/cameras/en/index.html?lang=en_US

iMovie 9 - cameras supported:

http://support.apple.com/kb/HT3290?viewlocale=en_US

iMovie 8 Camcorders supported:

http://support.apple.com/kb/HT1014

Digital camera RAW formats supported by OS X Lion:

http://support.apple.com/kb/HT4757?viewlocale=en_US

Digital camera RAW formats supported by OS X Snow Leopard:

http://support.apple.com/kb/HT3825?viewlocale=en_US

You could look at related articles for other information: