Connect to Windows2K Server VPN at 9600?

All of our remote access VPN clients are connecting to our newly-installed and configured Windows 2000 Server VPN. Clients connect via T1 to a 100Mhz NIC, into the Server which is a 500Mhz dual pentium HP Netserver with 550 Mb memory using PPTP. Theclients are all authenticating to an NT Domain administered by another NT4 server. All remote access clients have full IPX, IP and NetBEUI functionality, however, they all connect consistently at 9600bps, despite using Cable, DSL, or 56k modem.

Any ideas why and how to adjust?