Hi Jerry -

Luckily I found an earlier post of mine on this so I didn't have to re-type
it again . . .  :^)

First - I don't think you're going to get Voice & Video working behind ISA.
I haven't tried Video, but I know with voice that you can only accept voice
conversation requests, you cannot successfully initiate a voice conversation
from behind ISA.  This isn't so much an ISA issue as it's a NAT'ing issue.
If you absolutely need voice & video, I'd suggest using NetMeeting and
configuring h323 Gatekeeper in ISA.

By default, ISA includes a protocol definition for Messenger - but this
definition only allows for text chatting.  To allow the other functions,
you'll need to create a new protocol definition in ISA.  Open ISA Management
and navigate to

Servers & Arrays
   <servername>
       Policy Elements
           Protocol Definitions

Action | New | Definition

Create a new protocol definition (ie "Messenger - Full") that allows
outbound traffic on TCP 1863.   You also want to allow the following
secondary connections:

UDP Ports 5004-65535   Send
UDP Ports 5004-65535   Receive
TCP Ports 6891-6900 Outbound
TCP Ports 6891-6900 Inbound
TCP Port 6901 Outbound
TCP Port 6901 Inbound

Once you've created this protocol definition, you'll need to create a new
protocol rule that uses this definition.  If you confgure this protocol rule
to apply to Any Request (versus restricting to a security group/user
account), all clients should be able to use Messenger regardless of whether
or not the firewall client is installed.  If you opt to restrict this
protocol rule to security groups / user accounts, users will need the
firewall client installed.

HTH!