Sadly, Apple's been really stubborn and stupid about this. No, you can't really search for filenames. No, putting the term in quotes doesn't really help, since then it won't find stuff in the _middle_ of a filename. You _can_ hit Cmd-F in the Finder and have "name contains" as a secondary option. If you don't put anything in Spotlight's main search field and only in the name field, it kinda works. It's stupid, but it's just like that with Spotlight. Someone should hang for this at Apple.