Optical mouse acting funny with USB-to-PS2 converter

[BespinReactorShaft]

I've been trying to get my USB optical mouse to work with my notebook's PS2 port, using an adapter. This works fine on the desktop PCs I've tried it on. But it simply is not recognised on this Dell Latitude Pentium III notebook (not even the optical diode is on).

I've also tried using other optical USB mice with the same result.

Any ideas on what's going on? The mice work fine if I plug either PS2 or USB into their respective ports.

Thanks.