GolfScript, 94 characters

My first ever GolfScript program! This took me many an hour of fumbling around not really knowing what I was doing, but I persisted and I think I managed to learn the language basics and golf it fairly well.

Fully golfed:

[{}/8,{97+.3$-.*:>8,{49+.4$-.*:^2$+.[3<>^*4=>^=>^*!.2$|]"KNBRQ"8$?=*{[5$3$@]""+p}{;}if}/;;}/];

Commented and nicer source:

[
{}/              # tIn fIn rIn
8,{97+           #             fTst
  .3$-.*:>       #                  fDif^2 : >
  8,{49+         #                         rTst 
    .4$-.*:^     #                              rDif^2 : ^
    2$+.         #                                     ^>+
    [3<          # These    #                              [validK
     >^*4=       # checks   #                                      validN
     >^=         # do not   #                                             validB
     >^*!        # account  #                                                    validR
     .2$|]       # for null #                                                           validQ]
    "KNBRQ"8$?=  # move;    #                          valid
    *            # * does.  #                          validNotNull
    {[5$3$@]""+p}{;}if  # print? #  fDif^2
  }/;;           #        rIn
}/];

It may look like Claudiu's answer, which is because I referenced his answer, as well as my (unsubmitted) C solution, while making mine. He provided a good specimen of a (relatively) complex, working GolfScript program, and it helped me learn a lot about the language. So thanks, Claudiu!

Being new to GolfScript still, if you guys have any feedback, I'd appreciate hearing it!