vpn connection over dial-up connection

i'm trying to establish a vpn connection over a dial-up connection from a
windows 98 se machine to a machine running windows server 2003. the 98
machine is dialing into an isp and the server 2003 machine is on a high
speed connection. this works fine under windows xp. it also works if the 98
machine is connected to the internet using a high speed connection. it only
fails when the 98 machine uses dial-up, which is the situation i want it to
work in. i've created a vpn adapter under 98 which, as i said, works fine if
i use a high speed connection. the error i get when i try to connect using
98 is:

Error: 645
The Microsoft Dial-up Adapter is in use or not responding properly.
Disconnect other connections and then try again. If the problem persists,
shut down and restart your computer.

any help is greatly appreciated.


--
Gary Roach
ADB Services