Hi Paul--
A quick check to see if it's PostScript is to look at the first line. If it starts with "%!PS-Adobe-{version number}", then it's PostScript, and hopefully Ghostscript would be able to do something sensible with it.
PostScript files, especially ones from design programs like AI, usually won't have the text contents in human-readable form, because text may be stored with a custom (sometimes binary) encoding, and even if it is there in ASCII format, it may be broken down by individual characters so that each glyph can be placed precisely on the page. But Ghostscript is usually pretty good about sorting all that out and giving you back usable text, as long as the text layout in the original document isn't too wacky.
--Clay