Setup Mail Server on Linux Box

We're attempting to setup a Linux Mail Server through our VPS that will be a relay for a custom mailing system we've created. This is through remote login on a barebones VPS. You'll have full access to an newly installed server, and even access to re provision it with a different Linux OS (it has CentOS 5 now). We'd need a step by step of what you did to set it up as well. Should be a simple job for someone that knows what they are doing! Max $50. Payment after successful completion and test.