WPA2 Enterprise with Windows 7

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Hello

I am being thrown into a project head first and trying to get up to speed.

 From what I have read I need to have a certificate for using WPA2 
Enterprise. I would prefer not having to go to each machine spread 
geographically around a fairly wide area to install a CA certificate. Is 
it possible to use a purchased certificate so that Windows 7 recognizes 
it and will connect?

I think I only need one certificate for the RADIUS server, but still 
unsure. Does it work with multiple SSID's from different AP's? What 
about redundant RADIUS servers? Do I need a certificate for each?

I have googled and not seen anything definitive for these questions. I 
will continue to search, but hopefully someone who has this sort of 
setup working can answer those questions and I can carry on with getting 
it setup.

Thanks
Michael