Those small files are mostly viruses. Stay away from them, though being on a Mac you may not have much to worry about. Most full size movies are 600MBs or more. Smaller ones are usually inferior quality or porn. No movie file is only 240KBs, not even music files are that small.
Check files with
Bitzi Web Lookup before downloading. It'll help you sort out the good ones. While on the Bitzi site, search for the file there and use the magnet link to start the d/load in limewire. Then search for it again in LW to help find some sources for the file.
Also preview the file when it gets to 10-15% to check that it's what the title says and not mislabeled porn.
See:
Fake files showing up in search results,
How to find music(and movies).
WARNING: Viruses on network you should be aware of!