Just to make sure we're getting what you're saying... you have 2 macs, each with airport. No hub or base station. In other words, neither can connect to the internet via Airport. Is this correct?
And when you say "my source menu" what exactly are you referring to? Shared iTunes Libraries will show up in iTunes as "Other_Computer's_Library" where "Other_Computer" will be replaced by the actual name of the user account on the other Mac.
On the elementary tip, make sure that both computers have "Look for shared music" checked in their iTunes preferences.