I'm having the same problem, I think. My fn key
does work in Windows XP, since the function keys (f1 - f10) act differently depending on whether I'm holding fn or not. However, other advertised key strokes don't work. Specifically, fn + delete acts like backspace (not windows delete). Similarly, fn + left is not home, nor is fn + right the same as end.
My current solution is to use
http://www.autohotkey.com/ as has been mentioned elsewhere on the forum. I am using the script:
#Backspace::Send {Delete}
#Left::Send {Home}
to map command-delete to (in place) delete, and command-left to home.
For the record, my MacBook was purchased in mid February, before the very recent new rollout. I'm running XP with service pack 2, and the install is fresh as of today. I've installed the drivers that came with OS X, and have also tried reinstalling the keyboard drivers. I have updated my keyboard firmware, but I still have issues with keystrokes occasionally being lost when I switch points of focus. This information is provided to help people find a pattern as to what causing the problem.