duchess, are you using the lineage "Shortcuts" on the options panel?or are you using a proper software of the logitech mouse?
i reccomend you to use the logitech software, try to use the SetPoint® software , on the cd in the package of mouse.
here the links if you wanna download the software.
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32-bit S.O.SetPoint®, Windows XP, 32-bitSetPoint®, Windows Vista, 32-bit------------------------------------------------------------
64-bit S.O.SetPoint®, Windows XP, 64-bitSetPoint®, Windows Vista, 64-bit------------------------------------------------------------
try using this,
if you have any doubt with the mouse, tell us, or try to search on the Manufacturer web site
Logitech 