Matt -
I visited the RETS | RETS - Real Estate Transaction Standard site and took a look at this page also:
Variman User's Manual

I'm not getting it. Do you know anyone familiar with developing webpages with this type of programming?

It says it can be deployed on linux servers but that it requires a persistent connection to the database and mention PostgreSQL which I've never used.

I found this to: VieleRETS Documentation which seems to be the recommended one to use for php5...

Any thoughts or clarifications you can provide me would be greatly appreciated. I don't have a grasp on data feeds as it is...