That didn't take long - the Splinter Cell: Conviction demo Ubisoft was talking about yesterday will be released this week, on Thursday.
In it Sam infiltrates a warehouse and is asked to Rescue the Scientists. There's an Inside Xbox video detailing the content, or there's gameplay footage from the latter part of the demo on YouTube (be warned, this has spoilers).
There's no mention of a PC demo.
Splinter Cell: Conviction will be released for PC and Xbox 360 on 16th April. Thankfully, its lengthy development appears to have paid off. Catch-up with our Splinter Cell: Conviction hands-on to find out how.