Yes, MessengerFX is the online IM client for Yahoo, Gtalk, AIM and WLM (MSN). Perfect. You only have to access MessengerFX and enter login and password of the IM network.
Then, you'll enjoy all IM features as if you were using the common client, but online.
If you plan to use it as your IM client yu can even personalize it, edit groups and more.
A full featured web-based IM client for free.