For Word, Excel and Powerpoint files, all you need for viewing are <
icWord> and <
icExcel>. They work all the way back to OS 7.1 which, I believe, covers your OS of choice!
Some features may not be available without X, however...
When possible, convert thes things to AppleWorks or MacWrite and send them back telling the original author that you especially liked a particular portion of the file and you've made a few edits/notes they might want to consider.
Of course, you should also change/add ".doc" on the end, just to give them some fun...