Why didn't my Windows partition show up in the Startup Disk preference pane? I install Windows(XP after that 7) on my MBP with Boot Camp and every thing was fine but after a while in System Prefences -> Startup Disk my windows partition was lost and when I want to switch to my windows must restart my Laptop and Press Down option during startup. I can't switch directly from my OS X.

anyone know how can I solve this. or why this is happened?
Did you by any chance install the NTFS-3G driver?

It's a known bug (for quite some time, now). When installed, you can no longer have the Windows partition in the Startup Disk prefpane.