I'm trying to use this Python code:

import math
for i in xrange(500):
    x = 500 + math.sin(math.pi * i / 100) * 500
    y = 500 + math.cos(i) * 100
    x, y = int(x), int(y)
    win32api.SetCursorPos((x, y))
    time.sleep(.01)

taken from here to move the mouse cursor in an XP VirtualBox. The mouse icon will flicker to the appropriate graphic (when it hits the edge of a window it turns into the <-> resize image, for instance), but it doesn't actually move the visible cursor. I can move the mouse around while the code is running. Same result using the ctypes example in the above link. It works fine in the Win7 host.

I have Guest Additions installed, if that matters.