It is worth taking the time to write your sentences carefully. It's a little tough to interpret your core question:
Is this true it can be 5.5 even though it is labeled CS5 and also I see the files need to be converted to idml.
If your question if whether the Finder can say that a file is CS5 when it is not, then the answer is yes. The Finder will select an icon based on the file extension. (It may have additional information, but it may not.) The Finder's icons cannot be trusted for version determination.
If I try the CS6 trial, will the files be workable from 5.5 and then I need to backsave? Is this a good option or not suggested?
Also, this sentence question could be a lot more clear.
If you are asking whether CS6 files are editable in CS5.5, the answer is no.
Analagous to CS5 and CS5.5, if you wish to work between CS6 and CS5.5, you must save the file as IDML when working in CS6.
I think few would call it "a good option."
To do this I have to borrow a computer with snow leopard or whatever the animal is after mine.
You haven't told us what version you are using, but presumably it's not Snow Leopard, so it is presumably either Tiger (10.4) or Leopard (10.5). Providing this information is a good idea.
You should be able to install the CS5.5 trial by following the instructions at http://prodesigntools.com/adobe-cs5-5-direct-download-links.html.
Read the "Very Important Instructions"; do not skip directly to the links.
I'll convert a single file for you this morning if I get it in the next few hours. I'm sending you an upload link via PM.