“Rig" is the all-encompassing Vermonter term for a big toy- for example a truck or an evaporator used for boiling sap to make maple syrup. Or of course a honkin' computer! Playing some more with Vista 5381, I noticed this System Rating, giving my rig a 2 out of I don't know what. Note also that with Tablet PC functionality being built into the O/S (not an afterthought as we have today wtih XP), part of the system report identifies whether the hardware is a TabletPC. Funny, I thought we were calling them “Mobile PCs“ now. Hmmm.
So I clicked on the “Performance Rating“ link and got to this page which offered some information as to issues with my computer.
Since I shrank my screenshot (until I make a new one that fits on this page), the hazards say “Drivers are interfering with Windows entering sleep mode“ and “Drivers are causing Windows to start slowly“.
Funny I do have problems with sleep on this computer. 
I drilled into that but haven't done anything to affect it yet. I'm not to the point of mucking with the drivers at this level of detail. I don't know what someone like my parents would do with this, but a sysadmin or computer technician should be able to leverage that pretty well.
Without making any adjustments, I ran the “Refresh my Rating“ function since the average of 2 wasn't computing when looking at the numbers it was working from. Perhaps 2 is the default, but it wasn't correct - and therefore could be misleading if users don't know that theyneed to actually run the tool to get the “accurate“ rating. Now my computer gets a “3“. Still I don't know out of what. I did look at the help behind “what does this number mean?“ but didn't see it there. However, the help let's you give feedback and “Not enough info“ was one of the choices. Selecting that resulted in a text box where I was able to tell someone that it would be useful to know what the rating scale was. Oddly my two problems are no longer listed even though I didn't fix them. I better go add that to the beta feedback!
One point in the explanation is that Microsoft suggests using the rating to purchase software. So I'm guessing high demand games would have a high number and the assumption is that that number relates to whatever algorithm is used to calculate the rating of your computer. Hopefully, hard drive space doesn't outweigh RAM to give you a 4 on box with only 256MB in it.