How to I get MSN messenger to work through ISA?

Try this

Configure the Protocol Rule
Right-click Protocol Rule, and then click New Rule.
Type Instant Messenger Rule for the name of the rule, and then click Next.
Click Allow, and then click Next.
In the drop-down menu, click Selected Protocols, click MSN Messenger in the dialog box that opens, and then click Next.
Click Next.
Click Any Request on the Client type dialog box, and then click Finish.
Configure the Packet Filter
The type of packet filters to configure depends on the type of access you want to allow with Instant Messenger. First configure the packet filter to allow for simple Instant Messenger communication:
Right-click Packet Filters, and then click New Filter.
Type Instant Messenger Outbound, and then click Next.
Click All ISA Server Computers in the array, and then click Next.
Click Allow packet transmission, and then click Next.
Click Custom on the Filter type dialog box, and then click Next.
In the IP Protocol drop-down list, click TCP.
Under Direction click Both.
Under Local Port click Dynamic, change Remote Port to Fixed Port, and then for the Port Number type 1863.
Click Default IP addresses for each external interface on the ISA Servers computer, and then click Next.
Click All remote computers, click Next, and then click Finish.

On your workstation:
in the Messenger Client goto Tools-Options-Connection.

I use proxy box, DO NOT use HTTP

Use Socks Ver4 with the IP of your proxy (internal side) with the defaul port.

Hit apply, it should work.

Thanks and good luck
if you need more detailed help with your project i can be reached at support@brigadeindustries.com

This info can also be found at:
http://support.microsoft.com/default.aspx?scid=kb;EN-US;q277812

http://www.isaserver.org