In Windows 7, indexed search is almost unlimited in what it can do. You can specify almost any aspect of a file and indexed search will find it. To give you an example of the power of indexed searching, you could literally specify:
A .jpg file that was created using a Canon 20D camera at greater than 30,000 of a second, using flash, that was created before 6/25/09 and edited in Photoshop after 7\01\10 and has a Photoshop layer named "candy" that has a minimum of a 2 star rating.
Wow!! Pretty powerful stuff, huh?
You asked about specifying a file type, well, there you have it.
Non indexed searching is much like the old XP type search. When you finish typing your search and there are 0 results, click on the "more results" link in the results window and a new window will pop up that says basically, “OK, I couldn't find what you were looking for in my index so I present you with this window to look outside my index, click where you want me to search outside of the index". 99 times out of 100, you'll tell Windows to search outside your index in "computer". This little guy will search not just your local PC but it will search your entire system, including, external drives, flash drives, network drives, system folders, etc. The search will be slow, however, and doesn't offer the same search criteria that indexed search offers. You can search for file names and extensions only, no content or metadata searches.
If you are looking for a file that in not indexed but you get a bunch of indexed results, it's the same thing; Click the more results link and search the entire computer.