Speculation is that in addition to leveraging its existing assets and expertise in search technologies, IM would allow Google to complete a communication platform that includes Gmail (its Web mail system) and Orkut (its community networking portal). Reports also indicate that Google's IM platform and client would be based on the open source Jabber protocol.
The above screenshot mentions the name of the IM program as "Google instant messenger jabber alpha 0.068". This could be a prank as well.
Outside of speculation, there is a currently little known reality about Google's current IM capabilities. It actually already has an IM tool and it's publically avaialbale — it's not even a Google Beta or a Google Labs project. Google though its acquisition of Blogger last year also acquired a company called Picassa, which also offer an instant messaging service. The IM technology is called Hello and is currently focused on instant messaging between people to share pictures and now to post pictures to a blog. Hello is currently available only for Windows and uses a proprietary protocol.
See a full screen preview of Google Instant Messenger