More specifically, how do you hook up to an app that will be running on users local machines at localhost:####/somedirectory/someotherdirectory?
Where #### can be the numbers of their choice? Can they be relative urls for the httpservice?
You could use any url with any port as long as it is accssible through HTTPService and WebService flex components.
In a subsequent build, you should be able to use relative URLs in HTTPService Wizard.
The following might help:
If you are more interested in connecting to web service or REST service from Flex, this might help: