Pressing the Option key only displays the bootable volumes if you hold it down before pressing the power button. My normal practice is to hold down the Option key, then press the power button, and keep holding down the Option key until the boot volume icons appear.
As machead3 says, if the drive that's currently your default boot volume isn't the one you want, you shouldn't be fooling around with Option-boot; you should change the default boot drive in the Startup Disk system preference.
Okay, the Boot Camp thing is something we needed to know to begin the discussion. I think machead3 and I were both assuming that you were switching between two OSX volumes. Anyway...
The fact that Windows doesn't appear as a boot option suggests that the installed copy of Windows is not bootable. Both the Option-power trick and the Startup Disk system preference should display all bootable volumes; have you looked in Startup Disk to see if Windows (whatever_version) appears there?
There's some information we should find out before we get too much deeper into this.
1) What version of OSX are you using - 10.6, 10.7 or 10.8?
2) What version of Boot Camp are you using?
3) What version of Windows are you trying to install and boot from, and where did you get it?
4) On what disk and volume are you trying to install Windows?
Apple Boot Camp 4, OS X Lion and Mountain Lion: Frequently asked questions
Boot Camp has certain built-in limitations. It has to install Windows on the internal boot volume, and the OSX boot volume and the Boot Camp volume are on a single partition. If you have partitioned your internal drive into multiple volumes before running Boot Camp, the Boot Camp installer may not work correctly. The BC Assistant does its own partitioning as part of the install process.
You can boot from a copy of Windows installed on an external drive, but the Windows Startup Disk control panel will not see it, since Windows is designed to boot from internal drives. You'll have to use the Option-power trick every time you want to start up. Since Boot Camp will only install on an internal drive, you'd either have to remove the internal drive (with Windows installed) and put it in a USB/FireWire enclosure, or else clone your internal drive to an external drive using a GUI utility like SuperDuper!, Carbon Copy Cloner, or Terminal utilities like ditto or dd.
The minimum version of Windows that Boot Camp will install is Windows XP Service Pack 2; older versions of Windows can only be installed as virtualized environments. Officially, you're required to use a fully licensed retail install disk for Windows, not an OEM version (one that was bundled with a prebuilt Windows computer).
When you boot from OSX and open Disk Utility, can you see the Windows partition in the left sidebar? Unlike FAT32, OSX does not natively write to NTFS volumes. There are several NTFS-on-Mac drivers that will allow OSX to mount and write to NTFS volumes, including the Open Source NTFS-3g and the commercial Paragon NTFS for Mac. Once one of these drivers is installed, you can use Disk Utility to do some basic repair on the Windows partition.
If you can give us some more detail on where you are in the Windows install process and how you got there, we'll see if we can offer more help.