you can find instructions on how to set it up, here:
http://www.lullabot.com/videos/install-local-web-server-mac-osx
P
I would like to use an older Power Mac tower, likely a G4 or G5, as a web server for my forum. I would like to use free software if available, I've heard MAMP is a good option, but I wouldn't know how to go about implementing it. The server will be connected to my router and would need to be accessed from outside my own network.

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