One of the big problems with Safari is that instead of downloading .sitx files, it opens them in the browser window. One solution is to set your OS X Server to Prevent 'garbled text' file downloads via server settings. Of course, if you don't own Server, there's not much you can do.
On the client side, you have a few options. The first is to control-click the link and download it to the desktop. Unfortunately, there are times when the text is not a hyperlink. In those cases, you can copy the text, then open the Downloads window (Command-Option-L) in Safari and paste (Command-V) the download link.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050731130009795