Graphics card for multiple simultaneous users

[Felix Oxley]

Hi,

I want to set up an Ubuntu server (maybe Lubuntu) which the employees
in my company would use to access the internet instead of using
Windows & IE and becoming infected with viruses.

The users would either log on to a remote session using standard
remote X server & gnome, or by using one of the following RDP,VNC,
NoMachine NX server.
(I would probably configure the system and then make a live CD so that
the system would be returned to a known good state every night)

My current query is how the graphics subsystem driver & hardware etc
will handle multiple users simultaneously trying to watch YouTube or
BBC iPlayer?
(50 users total, say 20 (max) concurrent at lunchtime)

Will this be possible? What sort of graphics card should I use? Free
or proprietary driver? More than 1 graphics card in machine?
(I was thinking of getting a new Dell server with dual quad  core (16
threads) Xeon 2.8GHz processor, 24GB ram )

Any knowledgeable suggestions would be appreciated!

Thanks