Well, a true rumor has been making the rounds - Microsoft is no longer going to allow PC makers (including tablet manufacturers) to ship units with Window XP after June 30th. In case you didn't know, June 30th is the end of Microsoft's fiscal year and it is normal for them to end-of-life and product or license program around this time in order to "encourage" customers to upgrade.
So what does this mean for tablet PC owners? Not much unless your software doesn't play well with Vista. Anyway, PC makers will be offering a downgrade path but you'll have to go through the process of converting to XP from Vista yourself using recovery disks.