Hide IP with MacProxy?

I don't know what MacProxy is but you can just set a proxy in network settings.
Why do you want to do this??
Hiding you IP only works by using an anonymous proxy server as an intermediate but that kills performance because if you need to resort to free proxies.
If you need it for some websites only just use a second browser like opera that allows setting proxies without tunneling every HTTP traffic like you do with a proxy set in network settings.
For general use it is not feasible.

Free proxies you can google for but it is hard to find any that do work well are trustworthy and not too slow. It is easier to just join the tor network for security reasons. Tor is kind of a peer to peer proxy network that hops so many nodes that make it impossible to find the originating IP.