First create your "Input Device" in  /etc/X11/xorg.conf

Section "InputDevice"
        Identifier "Razer Lachesis"
        Driver "vmmouse"
        Option "Name" "Razer Lachesis"
        Option "Vendor" "Razer"
        Option "Protocol" "ps/2"
        Option "ZAxisMapping" "4 5"
        Option "Device" "/dev/input/mice"
        Option "Buttons" "7"
        Option "ButtonMapping" "1 2 3 6 7 "
        Option "Resolution" "2000"
        Option "SampleRate" "1000Hz"
        Option "Emulate3Buttons" "true"
EndSection

And let you Server know, that it should be loaded:

Section "ServerLayout"
        Identifier      "Default Layout"
        Screen          "Default Screen"
        InputDevice     "Generic Keyboard"
        InputDevice     "Configured Mouse"
        InputDevice    "Razer Lachesis" "CorePointer"
 

I didn't really test it, but on the first sight, the results look good. I will test it soon with some UT2003 matches on my box ...