IPSec NATTING and multiple firewalls

Hello,

I have the following problem:
there are several clients in an w2k network which have let
us asy IP adresses like 192.168.10.x with an netmask
255.255.255.0
The defaultgateway of these clients is a dsl-router on
which also an IPSec server resides and who is connected to
our ISP. The usage of this server is just to allow workers
to connect via SSH-Sentinal from their homeoffice to the
local network. As some customers have to be connected via
VPN too and there is no chance to setup these connections
on the router there is another firewall within the network
which is used as the gateway for these connections. On the
router NATTING is enabled for these connections, which are
then routed to the firewall I mentioned. How would you
setup the clients, to avoid secondary IP adesses on them?