I had the exact same issue with Panther. It affected a few pages in Safari (including Versiontracker), and a few email messages in Mail.app (only 2 out of thousands, as far as I could tell). The weirdest things about it: it's almost a phonetic interpretation of the text, in most cases -- the letters are just switched in really weird ways. Also, like mnkeybsnss said, if you copy and paste the text, it's spelled "correctly" -- i.e., text that looks like "hyyp://www.cmm.con" would turn out to be "http://www.cnn.com" when copied and pasted into the address bar. Because of this, I figured it was a font or encoding issue for sure...
After I installed Panther, I was messing around with FontBook and stupidly installed a bunch of old fonts. I think that one or more of these conflicted with each other, or with a system font. I solved the issue by deleting all the fonts I installed (I didn't feel like troubleshooting them individually), which seemed to work. A good way to test this would be to find a page that causes the garbled text, then change your default fonts in Safari >> Preferences... see if that works. Also, try changing the text encoding (View >> Text Encoding) to Western (ISO Latin 1). Let me know what works for you -- I don't know if you installed extra fonts or not, so I'm not sure that this WAS the real problem.