I recently installed Windows to a partition on an imac. I have to say, it's fairly painless if you just follow the directions provided by the Boot Camp Assistant on OSX. That said, I tend to complicate things by not following the directions explicitly.
One of the problems I eventually experienced was that the computer wouldn't obey keystrokes during the boot process. Things like:
option key -- show bootable volumes
c -- boot from cd
command + option + p + r -- reset pram
The circumstances that lead to this condition are: I ended up missing the time for the keystroke (must be held when apple sound is made) and instead of waiting for OSX to load and restart I pressed the power button. If you do this, there is a chance these keystrokes will stop working. The solution is simple: just turn off the computer and unplug for a while (seconds to minutes). That seemed to fix the problem for me.