How to integrate my Web Application with Skype, Gtalk of another IM system?

I want to be able to send reminders to my users, using their IM system of choice, very much like Remember The Milk does when it sends notifications.

How can I do that?

Additional INFO: I develop in ASP.Net, SQL Server 2008 and Windows 2008

From stackoverflow

• These may be overkill for your problem but these servers implement the Jabber (Gtalk etc) protocol and have add-ins which support sending messages over all the major IM networks.

  http://www.process-one.net/en/ejabberd/

  http://www.igniterealtime.org/projects/openfire/

  http://jabberd.org/

  You might be able to integrate one of them into your solution to solve your IM needs.

• gtalk is Jabber. Look for Jabber bots, there are some that will work in your environment. For example one in Python.

  Skype requires instance of Skype running on your servers, and your application talking to it via API.

  Each of the systems require its own approach. Thus your mileage can vary.

• Just as an FYI, the GTalk servers also require Transport Level Security (TLS) so make sure to look for that in any library you are considering for your XMPP communications.

• As mentioned above you could use your own jabber server create an account on that server and then add a gateway for each IM protocol you wish to support. This way, you use a jabber api to send messages on one account (your local jabber account) and then the server will pass through the gateways to the various protocols.

  Another way to do this would be to use libpurple. This is the library used to power the multi protocol support in pidgin and adium. This way would have less setup but maybe higher learning curve.