The quote from the news story about Yahoo vs. New Corp possible alliance says the following:

Yahoo Inc. is discussing a possible partnership with News Corp. in its latest effort to repel Microsoft Corp. or prod its unsolicited suitor into raising its current takeover bid, according to a person familiar with the talks.
The specifics of the joint venture still hadn't been worked out, said the person who didn't want to be identified because of the sensitivity of the matter.

A popular webmaster forum webmasterworld.com has initiated a discussion on the matter and so far it's not clear as to how is this alliance between Yahoo! and News Corp going to help shareholder value? I don't get it.

Earlier Microsoft had made a hostile bid for Yahoo amounting to 45.5 billin dollars, which Yahoo! formally turned down.

It is probable that either Yahoo! has received a better offer from Murdoch or is seeking another alliance to repel Microsoft's Bid.