Is there a Mac equivalent to Windows 7's library feature?
Easiest way I can think of to do it is if you bring up the file info window by pressing ⌘ + i keys, and then add something into the Spotlight Comments field that you keep the same through the files you want. Rinse and repeat for the files. Create a new Smart Folder, for the search option go to Other... and it'll bring up the full list, which will include Spotlight Comments.