UPDATE A Barnes & Noble exec is reportedly saying that the bookseller isn't part of Microsoft's announcement happening this evening.

The event, which Microsoft is being incredibly cagey about, is being held in LA, but journalists going to the big reveal haven't even been told where in the city it is being held. 

"Dow Jones reports that the speculation that Barnes & Noble is a part of today's announcement is 'not true at all'. (We saw this nugget from our Bloomberg terminal. When a full version of the Dow Jones story is up, we'll link to it.)," reports Businessinsider.com

Over the weekend, a report on TechCrunch and other sites reported that sources suggesting the company would announce a new Barnes & Noble Nook tablet running Windows 8.

Reports on Twitter suggest this isn't the case. 

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Hours away from Microsoft’s “major announcement” and we’re still none the wiser. That hasn’t stopped speculation mounting, however, with rumour of a tablet device continuing to rear its head. 

Yet perhaps we should lower our expectations, with an eBook reader seemingly proving more likely rather than a Windows 8 tablet, with Microsoft said to have teamed up with Barnes & Noble for the big unveil.

Microsoft invested $300 million into Barnes & Noble in April of this year in a partnership it dubbed “Newco”. So far that’s been it, but sources are saying that the Los Angeles event, scheduled for 3.30pm (Pacific time) could be their first joint venture.

Barnes & Noble is one of the world’s biggest book retailers and has produced eReaders in the past. A collaboration between Microsoft and them would suggest an eReader type device is more likely than all out tablet, though it could have one stand-out card up its sleeve. 

According to one source, it could be the first non-Xbox device to have the ability to stream Xbox Live. Until 11.30pm tonight then.

What do you think Microsoft's "major announcement" will be? Let us know.