If you can't change it in Mandrake then you have 2 choices:
Re-install (a pain in the ass!)
or change a few lines in the /etc/X11/XF86Config file.
You need to go to the section about 'pointers' and change the two parameters protocal and device so that Mandrake knows what you want. I would use emacs in a console environment.
Press Crtl-Alt-F1 all together you should see a text login point. Login as root.
and then press: Ctrl-x and then Ctrl-F
You then have to delete everything from the line below at the bottom, and then type:
You should see a load of text already there. Go down to the pointers section and change the things I said to what you want. To save the file:
Ctrl-x and then Ctrl-s
To exit: Ctrl-x Ctrl-c
Restart and you should have a functioning mouse.
Goto the Mandrake website and ask them what you should put in those two lines, or someone else may know.