As a recent Mac convert I am finding I love the native Mac apps. Turns out, you can get iChat to work on just about any network. Here's how...

This actually isn't too hard to do. It leverages Jabber servers with gateway addons. The only trick is that iChat doesn't have the ability to browse/register Jabber services so you need a different Jabber client. I used Adium.
* First, in Adium register a Jabber account to this server: inflecto.org

* Once you do that then in the "Adium" -->"Preferences" --> "Accounts" highlight the newly added "inflecto.org" account (typically @inflecto.org)

* Right click on it and select "Discovery Browser"

* click the little arrow next to the "Openfire Server" word

* double-click the services you want. If you want GTalk, you'll need to add that since iChat will only let you do 1 Jabber account (and inflecto.org counts as 1). This server has AIM, MSN, Yahoo, GTalk, ICQ, and IRC installed. As you double click the services it will ask for login info and then it will add the service.

* Once you've added all your services just quit Adium and fire up iChat.

* Add a new iChat account - Jabber

* Give it the "@inflecto.org" and password. use "inflecto.org" as the server name.

* Make sure to check "Use This Service" radio button to login and you're done!

Cheers!