Do you want to run the remote clients in their own subnet, different
from the LAN subnet?
That is a good idea, in my opinion. You get "real" IP routing between
the remote clients and the LAN. (If you use the same IP subnet you are
relying on the server to act as a proxy for the remotes). You use a static
address pool in the RRAS server, as Bob suggested.
You enable IP routing on the RRAS server. Apart from that, the normal
routing rules apply. The remote clients will use the RRAS server as their
default gateway. If the default gateway for the LAN is not the RRAS server,
you will need to add extra routing on the LAN to get the traffic for the
"remote" subnet to the RRAS souter.