Microsoft went backwards with search capability in Windows 7, IMHO. It may be possible to do lots of things, but it is not always clear how to go about doing them. I found that I too had only Date and Size. However, more options appeared after I typed a keyword and did a search, then clicked in the search box again.

However, it works to do:
Search words type:=.doc

Or from a different angle:
Search words kind:=document

"Search words" is the stand-in for the word(s) for which you are searching.