How do I configure MSN Instant Messenger to work from behind the ISA Server?
The easiest way will be to use the Firewall client to dynamically allow access using whatever ports it uses.
If using S-NAT you will need to create a protocol definition with that port info... (55xx? )
If you plan to use Netmeeting you may need to configure the ISA gatekeeper section and also set netmeeting to use the gatekeeper.
Usually when netmeeting is using gatekeeper, the remote NM client has to set their NM to use a gateway, unless they too are behind a getekeeper and their gatekeeper is configured properly to route calls to your GK.