Concerning formatting:
When you use Boot Camp Assistant to create the partition, it uses FAT32* format. AFAIK newer versions of Windows will not install on FAT32. They have to reformat to NTFS before installing.
Concerning booting back into OS X:
Assuming that you did install Windows correctly onto the partition labeled BOOTCAMP, then OS X is still there. While in Windows, open the Boot Camp Control Panel (you did install the Boot camp drivers from the OS X DVD, right?) by clicking on the grey diamond in the system tray. On one of the tabs there is a setting for start-up disk. Likewise, there is a similar setting in System Preferences under OS X. I believe that either of these settings should change the default operating system (I've never actually changed mine from the OS X default).
You can also choose which operating system to run when you start up the computer. Hold down the Option (Alt) key just after the start-up chime. After a couple of seconds, hard disk icons for OS X and Windows will appear. Choose the one you want to boot to. This selection is temporary (unlike the start-up disk settings in the previous paragraph), so it will not change the default operating system.
I hope that helps.
*FAT32 needs to die a fiery death, along with other dinosaur technologies (such as interlaced video). /rant
