Open help (Start Menu => Help) and search for "Incoming Connections". In
the "Overviews, Articles and Tutorials" section you should see an Incoming
Connections article. This should give you some background information and
instructions on how to configure incoming connections. You will want to
turn on VPN connections in the Incoming Connections wizard, there is a
separate page for this so it is hard to miss. The cable modems should not
be a problem unless they are also router/NAT devices. In that case, you
will have to configure port forwarding so that the the incoming VPN request
is forwarded to the right machine. It will also help to have a static IP
Address from your ISP for the "server" machine so you can easily reach it
from home. A dynamic address will complicate things unless you have dynamic
DNS for the machine.
See the docs for your NAT/Router, if you have one, to configure it to allow
TCP 1723 and GRE packets to pass (for PPTP). You may also need to turn on
PPTP pass through on the client side router/NAT device. The windows
configuration is easy, unfortunately the network configuration may be a
little more difficult. Your Win98 machine will have a help topic on setting
up a VPN connection entry in the Dialup Networking folder if you need help
with this.
Hope that helps,
Quintin
