You don't say how what version of the Mac OS you have on the old machine. If you have ClarisWorks/AppleWorks, you should be able to do a save-as operation on each of your ClarisWorks 4.0 files and convert them to either some (old) version of Word or to RTF. Assuming these files don't contain excessively fancy formatting, RTF should work fine. If you're going to transfer them to a PC, save each file with a filename ending in ".rtf" or ".doc" so that Word will have an easier time recognizing them as files it should open.
If you can't do it that simple way, you might need to purchase something like MacLink Plus from Dataviz <http://www.dataviz.com
If you want to run a word processor as opposed to converting the files and transferring them to another machine, ClarisWorks/AppleWorks 5 will work and if you're running Mac OS 9 you can get AppleWorks 6. You should be able to get a copy of Microsoft Word/Office 2000 used on eBay if your're running Mac OS 9. Office 98 you can find at bargain prices on eBay and it works just fine and might be a better choice if you are running Mac OS 7 or Mac OS 8 on that machine.