You can't password protect individual partitions. You can password protect User Accounts, boot up, system setup, bios, and individual files and folders.
Listen, I am far from an expert, but I have read the book Windows XP Inside Out, by Ed Bott and others, several times over, and I do not remember anything about an ability to password protect a partition. If I am mistaken, and I don't think I am, I do apologize sincerely. I have rechecked the book as well as Vista Inside Out, by the same authors, and nothing is there either about this ability. I am pretty sure this would have been included in the books, because everything else is, including using Group Policy, and Repairing or Reinstalling the OS.
If you wish to stop anyone from even booting up Windows, you can set this password in the motherboard settings. Each computer manufacturer uses different key combinations, mine uses the F2 key, to enter setup. Often, while booting Windows, you will see directions on how to enter the bios and/or the system setup screens. When you see the key combination, just start tapping it gently, and you will soon enter that area. If you see the Windows Logo, you missed it, just turn off again, and start over.
Hope this helps out some, sorry I wasn't able to tell you how to password protect a partition. Please have a nice evening.