Connect to a Proxy

[Daemn]

Hey everyone, I'm making a php script that will let a person enter an address, and my server will look for a working proxy to load that address with.

So say http://mysite.com/proxy.php?url=http://google.com/ would load http://google.com/ through a proxy, but if the proxy was down it would try a different one.

Can anyone kindly direct me to some code or tutorial or doc that might help me do this?

Thanks very much in advance