I have a similar setup. I have a 12" PB and an IBM X31 (which is almost exactly the same size). I walk to work most days and use one 12" Mac Sleeve (apple.com) and one Shinza ZeroShock sleeve (
http://shinza.com/product_info.php?products_id=45 ). I put both of them in a ChromeBags Mini Messenger, which can hold them with a bit to spare.
http://chromebags.com/minimetro.php (Ironcially the IBM is in the Apple sleeve and the PB is in the Shinza.)
That solution when you sum it all up is a little expensive but I can carry both laptops, power, PDA and misc nick nacks comfortably a mile twice a day.
When I go to clients I either switch to my APC bag which I can not find a link to, or my blackbox bag
http://chromebags.com/blackbox.html
Both the blackbox and the APC case can fit 2 12" laptops but not with much room to spare. I usually only switch to those when I am going to a client or am wearing a suit. Of the two I prefer the blackbox, but I have a reputation for being a little off kilter. Both can pass in a professional environment but the leather APC bag raises less curiosity.
There are other options, especially when you go into the executive briefcases like this
http://www.amerileather.com/50-0.html . It just depends on what you like I guess.