This is an excerpt from Michael Robertsons Minute
"Google is announcing new instant messaging/VOIP (net calling) software called Google Talk. Google's plan is sure to get considerable attention as reporters chronicle Google's efforts to play catchup to the instant messenger leaders like AOL, MSN and Yahoo!. But there's something much more noteworthy about the announcement. Google is agreeing to connect to other networks - something the big three instant messaging companies have refused to do."
You must have a gmail account in order to use the software but I am hedging my bets that this becomes a huge thing when released out of beta. Make it work under Terminal services and they will really have something here.