Ubercart-based POS / Kiosk
I'm working on a similar problem.  I have an ubercart based shopping system that a customer wants to have available on a public computer in his store.  We need to change themes, branding etc and auto-logout users.  His users will also be ordering from home, so we have to identify that particular computer and change the behavior and look of the site when we know they are ordering from the in-store kiosk.

Kiosk module that may help

This module allows an administrator to put selected computers into "Kiosk Mode".
"Kiosk mode" simply means that a given computer will have an extra flag set for template files, which allows a themer to exclude certain page elements, such as off-site navigation. 

I'm installing this on my test server and we'll see how well it goes.  I'm hoping to figure out how to get that variable (if $kiosk) into ubercart checkout conditions and trigger some actions based on it.  It seems like themeing is pretty easy with this module but as for changing behavior, I'm not super sure how it will work.

Please let me know if you find any magic bullets as we're both trying to do a similar thing and i'd be great to share a solution.

UPDATE: I've been working with kiosk mode module (drupal 7 version) for a bit and have been able to create custom rules by calling the kiosk_is_kiosk function defined in the module. Simply use custom php condition in rules with this code: 

 return kiosk_is_kiosk();


And you can have different workflows for kiosk terminals than for regular on-line users.  So for example, once an order is finished the kiosk will log out the user, but not a person using the same site from the home.

-Zachary