For XP do this, dunno if its working on windows 7
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Control Panel\Mouse]
"MouseSensitivity"="10"
"SmoothMouseXCurve"=hex:\
00,00,00,00,00,00,00,00,\
00,00,0A,00,00,00,00,00,\
00,00,14,00,00,00,00,00,\
00,00,1E,00,00,00,00,00,\
00,00,28,00,00,00,00,00
"SmoothMouseYCurve"=hex:\
00,00,00,00,00,00,00,00,\
00,00,38,00,00,00,00,00,\
00,00,70,00,00,00,00,00,\
00,00,A8,00,00,00,00,00,\
00,00,E0,00,00,00,00,00
I have set up a new machine and used this and it works as well as confirmed by others.
Open textedit, paste it and save it as imustdoubleclickthis.reg . Say yes and reboot.
Or go to [HKEY_CURRENT_USER\Control Panel\Mouse] with regedit yourself and edit manually.