Interact with GTalk from webpage, use gtalk: commands.
gtalk: command list
<a href=”gtalk:chat?jid=[USERNAME]”>Contact me in GTalk</a> — For Chat
<a href=”gtalk:call?jid=[USERNAME]”>Voice Chat</a> — For voice chat
Replace [USERNAME] with you gmail ID. and end user must install GTalk.
Get more IM’s details here http://shareourideas.wordpress.com/tag/embed-ims-in-website/