I think I understand what you are asking. Let me know if this works.
Say you want to search for jpg files on drive F:. All you have to do is go to Computer (or Explorer) and browse the root of that drive (I mean just double click the drive or expand it). You'll notice at the top of the Explorer file browser there is a Search field. Enter your search there and hit enter. It will only search whatever drive you are currently in. There are additional filters you can select when you are entering something into the Search field.
I guess the key is you have to be within the part of your hard drive/partition/folder that you would like to search and then use the Search field in that Explorer windows. Another example is if you wanted to search all drives on your computer, go to Computer from the Start menu and use the search in that windows... It'll search all drives (A, C, D, E, etc).
I hope that helps. The same thing frustrated me when I went from XP to Vista, and I felt stupid when I finally figured out how to use the new search system.
BTW indexing your drives for searching is really helpful if it is a permanent drive in your system. It'll make your search results come up near instantly.