Is W2K Server a viable VPN Server?

My client has a tiered T1 line at their head office.

They have three satellite offices in different cities, with approx. 4
computers at each office, and each office has either a 128KBPS ISDN line, or
a cable modem.

I want each office to be able to access the head office exchange server
through outlook, save and open files on the head office server, and access a
Citrix Winframe server at head office.

Will adding a Win 2000 member server set up as a PPTP server provide a good VPN in order to have each client access the resources listed above, or is it
not a stable / fast enough solution?

Thanks in advance for ALL advice,

Gavin