Ballmer at CES last year

[Update: The keynote got under way around 7 p.m. after a power outage that shut down the main stage.]

LAS VEGAS -- Microsoft CEO Steve Ballmer will, in fact, show off a new HP slate computer during his Consumer Electronics Show keynote address tonight, according to the company. But the unveiling appears less about Microsoft plunging headlong back into tablet computing, and more about Microsoft showing what computer makers are doing with Windows 7.

Ballmer's speech is getting under way shortly at the Las Vegas Hilton. Among other things, he's expected to tout Windows 7's progress since its public release in October. And as part of that, he'll show a number of computers that run Windows 7 and take advantage of the new operating system's features.

That's the context in which Ballmer is expected to unveil a new slate-style PC from Hewlett-Packard. It's a Windows 7 machine scheduled to be available later this year, with strong battery life and a multitouch interface. Other details, such as pricing and hardware specs, weren't available in advance of the keynote.

Tablet hype is running rampant in the industry right now, given reports that Apple is set to debut its own tablet device later this month. Microsoft's decision to feature the HP slate in the keynote may well be a reaction to that, but the device to be shown tonight is not a case of Microsoft, on its own, attempting to directly challenge whatever Apple might release.

Word of the HP slate first surfaced last night, when the New York Times' Ashlee Vance reported on its expected unveiling. AllThingsD's Kara Swisher reported earlier today that it's not the much-hyped "Courier" tablet-style device that Microsoft is reportedly working on.

Also at the keynote, Microsoft is slated to announce that Project Natal, its motion-sensing game controller for the Xbox 360, will be released later this year, in time for the 2010 holidays. In addition, the company will preview Game Room, an upcoming Xbox Live service that will let people compete in a retro arcade. More details on those announcements in this earlier post.

Microsoft is also expected to announce a new version of its Mediaroom IPTV software, with features including the ability to extend content from the television to PCs elsewhere in the house.

On the mobile front, the company will show a thin, new Windows Mobile 6.5 device from HTC, the HD2, to be available on T-Mobile, with a 4.3-inch touch screen. But contrary to my earlier speculation, it's saving any bigger Windows Mobile news (Windows Mobile 7, maybe?) for the Mobile World Congress next month in Barcelona.

I'm in the audience the Ballmer keynote, and I'll post more details as warranted. Microsoft is also streaming the keynote live on this page if you want to tune in.