Windows 64bit can handle 32bit stuff no problem since it comes with all the 32bit stuff included. The BOINC client is really just a wrapper to run the various science applications. Normally you will get 64bit stuff in preference to 32bit on a 64bit system, but not always so for your setup this is nothing unusual. Currently I'm getting CEP2 units on my 64bit linux rig. The difference being that I don't have 32bit anything installed on my system. I've spent some time checking this to be sure nothing snuck in as I've always intended this to be a pure 64bit machine ... and yet I'm getting 32bit CEP2 units and they're running properly.