Your simplest solution is to just run CentOS 5.3 in a VM (e.g. Sun VirtualBox). This requires minimal setup, has quite reasonable overhead (assuming an Intel Mac), and you’ll be able to actually test and debug what you are building.
If you really insist on cross-compiling, you must build a cross-compiler. Instructions are here and here, but beware: it will likely take you several days to get it right, and then you’ll still need a VM to test the result, so I don’t see any point in doing it that way.