Well, first back to the "pro or not " issue.
In the LW window on the right top you should actually see the word PRO.
I'm curious, where did you get your pro version from? From the official LW site:
http://www.limewire.com/
To your question about the songs, from my experience I would say that some people share also their Incomplete files. When those people preview files they are downloading by themselves, LW will make a "preview file" marked with a long serial number (some start with a letter such as "T") followed by the title of the file.
And now it looks that you have downloaded exactly such a file with only a few seconds or a few minutes contents.
Always check files either with Bitzi (right click on a file in your search window, go to advanced and then chose "Look up with Bitzi"), or look also at the file size. Songs usually mp3 files should have some 2-5 MB or even more. Files with less than that aren't worth to download.
