Lost Windows after repartitioning with Disk Utility
If you resized Mac OS partitions creating new partition after installing Boot Camp and lost Windows in boot option, you can recover it back with following steps.

If your Boot Camp is Windows 7:


Insert installation disk for Windows 7, boot to it, and start regular Windows install process.
Keep going until you see a screen saying "Install now".
Choose the option below the Install button: Repair your computer.
On following screen select first option: Startup Repair.


When done, reboot holding Option ⌥ - the Boot Camp partition is back!



If your Boot Camp is Windows XP:


Boot to OS X.
Go to your Windows XP partition.
Locate in the root directory a file called boot.ini.
Open it with a Mac text editor.
Look for part that says partition(x)
(x) represents the number of your Boot Camp partition. Now, you should add 1 to the number. Example: partition(1) should become partition(2)
Save the file and close the editor.


When done, reboot holding Option ⌥ - the Boot Camp partition is back!