I have a very new iMac and had Win 7 installed on Bootcamp with minimal trouble and it's been running great, had it set up so that if I just restarted it would automatically boot Windows. Awesome, I love Mac. Problem now is, I just installed Mountain Lion and not only does it not auto-boot to windows, I can't get the Dual boot screen (holsing Option after restart) at all. I've tried several times to make sure that Option is regestering upon startup, and it's all good.
I usually have good luck finding answers to stuff like this on the forums but I'm not seeing any cases exactly like mine yet. I would love any advice anyone can offer and I'm happy to provide any info about my system that could help.
Why not just try Windows 7 DVD and boot that, maybe you need to edit the BCD was all.