Shawn,
Unfortunately Simple Edit (like Teach Text) can't open even modest size files, and can only open plain text files. If this file was sent to you say from somebody using OSX and Text Edit, then it may be in a number of formats, including rtf.
BBedit Lite was a popular pre-OSX utility that let you open all kinds of text files. As Simon said, there's lots of them out there, though some may let you open just about any file with text (and also show you all the buried formatting codes) and some will just do plain text. Also, just about any word processor should let you open your file.
Brian