Jim is right, unless you are a pro databases can be overkill. You can name your files with the specific subject and or date, eg 20080420_sunset.nef. You can time stamp this as automatically as well with ViewNX or Breeze downloader.
Then do a file search for sunset and you will find them. I also use Thumbs Plus, but the search function is very clunky and you need to be a programmer to understand it.
On another note, does anyone know if there is s/w that will mirror one drive automatically (raid hardware not to be used) and then back up the second mirrored drive to a third drive?