After you have installed Parallels Desktop and booted for the first time into the Boot Camp Windows partition via a virtual machine, you can continue booting into this partition as usual, via Boot Camp. The Parallels Tools installation does not affect Windows operating system itself, it only helps you work with this operating system via the virtual machine.
To boot via Boot Camp partition:
Warning: Before booting into the partition via Boot Camp, make sure that the Boot Camp virtual machine is stopped.
Troubleshooting
When booting into Boot Camp, you may get a black screen with the choice of two configurations:
You may get an error message about a computer disk hardware configuration problem.
To troubleshoot a problem:
Anyway, you can connect this partition as a data disk to any Windows XP or Windows Vista virtual machine.