VPN connections

There seems to be a debate in my staff about the bandwidth used by each VPN connection. If we have a T1 line to the Internet and 5 users connect via 256K DSL, will one user suffer slow speeds, not connect at all, or not even be affected? Our general internal network pushes packets of data as needed, and some believe that a VPN connection is no different, if you have T1 bandwidth available, then 10-15 sites can ride the VPN (each with 256K DSL connections to the Internet) without a problem as long as they are not all collectively sending more data than a T1 pipe can handle. Who is right?