My mission should I pull it off: find away for multiple users to see and edit sales/ inventory quantitys in real time. (Envision all the screens at the NY stock exchange but smaller)

Current Ideas:
Shared desktop/ application shareing (multiple people connected to same spread sheet concuremtnly) looks like a dedicated "desktop" will be required given what I have seen form the solutions bellow:

MS Live meeting (kind of what I want can it be done with out goin out side my firewalls? at what cost?)
MS Share point (near real time, mearly a collaboration tool)
Net Meeting (same as live meeting, but i got it to work internaly, but its to complecated for the users)
VNC (would only allow one connection at a time, how to enable multiple views of same session?)

I had/am conssidering:
RSS web page but how to update from the web page without coding the entire app? (can i even do this to a file?)
Lotus notes application shareing
a VB front end to a spread sheet or Access database file?