Emulate three-button mouse(macintosh)

How can I emulate a three-button mouse from a macintosh one-button mouse?The Debian 3.1 standard X installation does not provide this kind of emulation.In SuSE-PowerPC I needed to edit a file but I don´t remember anymore the instructions to do it.

Warning in XFree86.0.log

The Debian X Configuration tool was not very effective configuring my system(iMac PowerPC,first generation, running Debian Sarge),a black screen that´s what I got. So,I needed to extensively edit the XF86Config-4 file and now KDE,GNOME run perfectly well,the only thing is: -when I read through /va