You can use contextual menus to copy files in the Finder. Control-click on the file you want to copy, and from the pop-up menu, choose "Copy [filename]". Then, in the folder you'd like to copy the item to, control-click in some whitespace and choose "Paste item." The entire file will be copied. If you choose "Paste" in a text editor, only the name of the file will be pasted.
[Editor's note: This is truly a 'copy' operation; the original files are left untouched. If you are trying to move the files, then remember to delete the originals after you've verified that the 'paste' worked successfully.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20010929184814910