I have windows installed with boot camp and when i boot into mac osx leopard, and install the parallels, it wont let me click "Use Boot Camp" it's so troublesome. boot camp on my windows detects my mac osx but when i go to my computer on my windows it doesnt detect the mac osx hd. WHAT THE HECK?!
That is normal, BootCamp windows cannot detect OS X. As to Parallels not allowing you to select the box, do you have an existing BootCamp install.
Do you have any other installs of Windows on your computer that you would like to keep? If not, search for files with the extension .pvs, and then delete the resulting files.