From: DeskNow Knowledge Base
http://www.desknow.com/kb/

Can I connect the messenger to MSN, Yahoo, ICQ, AIM
http://www.desknow.com/kb/idx/8/012/article/

DeskNow supports the Jabber protocol, a popular protocol used by many instant messaging application.

The integrated DeskNow Messenger (the instant messagiong client that is embedded in the DeskNow web page) can only connect to your DeskNow server. This ensures maximum security and ease of use for most users.

If you want to use the same messenger to communicate with your DeskNow contacts and with people on other networks (like Yahoo Messenger, MSN, AIM, ICQ), you can use an application like GAIM (http://gaim.sourceforge.net) . GAIM is available both for Windows and Linux.

See this article for instructions on how to configure GAIM to connect to DeskNow.