I feel certain that Subaru has a code in the VIN for AWD vs FWD.....but you'll have to find out what that is.
Meanwhile, there are a bunch of VIN decoders out there- some will try to charge you for the info, while others will let you do one or two per day for free, and only charge for quantity.
A quick search comes up with these (YMMV):
http://www.analogx.com/contents/vinview.htm
http://www.is-it-a-lemon.com/vin_check/content.htm
(this one has a really good explanations of what makes up a VIN)
http://www.oakos.com/wrx/vin.htm
(this one is for a 2002-2003 Impreza, but it clearly states that the 11th digit is the tranny, just need to figure out what codes will apply to your car)
http://en.wikipedia.org/wiki/VIN
(this one gave me a headache.)
Bret.