How can I correlate a wall jack to a user/machine on the domain?

Interesting. You'd need a custom web application to associate and present the data - I'm sure Valve doesn't have a problem with this.

I'd envision it like this, in the simplest case:

• Have a database that associates a user's name to the MAC address of their computer, that gets updated when someone's computer changes or a new user is set up.
• Configure your switches so that a description or label on the port conveys something useful about its location; r102.d004 for Room 102, desk 4, or something like that - something easily machine parsable.
• Have an application sweep the switches every few minutes. Grab the MAC address from what's connected on the port, and the description on the port.
• Use that data along with some nice map graphics that associate r102.d004 to a physical location, translate that MAC address into the user's name with your user database, and present it in a pretty interface.

if you use 802.1x, then you may want to adjust to use that data instead - and I can envision doing this with wireless access points to get the approximate location of someone's wireless client as well. Good luck!