Microsoft's Risky Tablet Announcement
I think you've (closely) described the OLPC laptop: http://laptop.org/en/laptop/hardware/specs.shtml.
With some minor design changes, these guys could probably become a major player in the quickly-heating-up tablet/slate market.
Reliable, Free Anti-Virus Software?
Not necessarily - There are a number of Dell laptops whose wireless hw does not have drivers available for Ubuntu. Broadcomm BC43xx? Ugh! Been there. There are fixes documented out there, but it requires some effort at the console (pkg installs + some config changes) to pull it off. Not guru-level effort, but certainly enough to scare off or irritate most newbs. Consider also that this person may already have a significant collection of Windows SW that they wish to continue using.