debian on domain clients ?

[fluppe <debian@searo.be>]

Hello, 

I am working for a while with debian without problems, everything works
as it should work!
Now, we want to start in the company to transfer CLIENTS that now work
with windowsXP to LINUX!

My first thought is of course debian, but the clients have no direct
access to internet and i can't allow x number of clients to connect to
internet but how do i have to do the upgrades and the installation
then ?

Is it possible that i download with one server all the debian software
and that it reguallary checks for updates and then syncronizes ?
And that my client can update via that one internal server ?
if yes, how can i do it ?

cheers,
Phil.