Lerameur,

Multiplications with negative numbers works but if you need division you need to do a little "manual" work:
Code:
Sign VAR Word       'This will hold the sign of our value.
Left VAR Word
Right VAR Word
Temp VAR Word

Left = 100
Right = 200

Temp = Left - Right     'Temp is now -100 (or 65436)

If Temp.15 = 1 then    'Highest bit set means value is negative
   Sign = -1
Else
   Sign = 1
Endif

'We cant divide a negative number so we have to use the ABS operator.
Temp = ABS(Temp) / 2    'Temp is now 50 (positve)

Temp = Temp * Sign       'Re-apply sign, Temp is now -50 (or 65486)
/Henrik Olsson.