Thanks for answering.
There are no W2K drivers at logitech.com for this mouse. The setup would not install reporting "wrong os - go to logitech.com and download correct driver". I copied the cd contents to my hard disk, unchecked read only for the config.ini file and changed WIN2000=FALSE to WIN2000=TRUE in the "uninstallable" section. This allowed me to go through the setup but my system never did detect the mouse as anything other than an HID usb mouse.
I just read that the button above the wheel cycles between 400, 800, 1600 dpi out of the box so that will probably be sufficient for my needs. I don't really have to have the programmable stuff, although game profiles and assignments would be good. I'm hoping that they will have drivers/support for W2K soon. The razer diamondback is another alternative, but I can't decide. I like the feel of the MX518 and I've heard a lot of reports of loud clicking problems with the razer which would drive me nuts.
Mouse reponsiveness in gaming is radically improved over the MX510. I like the mouse a lot, but I'd like to see what the software package has to offer.
It's hard for me to believe that Logitech has given up support for W2K.