Help on Connecting analogue modem to RAS server

Hallo, First timer on the group.......... dont know how to
start.......... guess will just explain what I am trying to do........

I am trying to replace a solution where serial devices connect to a Win
NT server via Dial up analogue modems using PSTN.

The solution we are trying needs Ethernet connection to the devices.
And so
I am trying to use win 2k RAS server connected to 8 x modems via PCI
Cards attached to PSTN Lines.

we have connected a netcomm modem attached to a 4 port dlink router on
the dialling side, this setup works well with out the encryption.
But when I add encryption to the modems, this setup does not
work........

I am lost now................. could any one help please

Regards
Samir