CPL mousefix is not necessary, and fuckin with Windows registry is never a good option.
1 ) Set Windows sensitivity to middle (any less/more will amplify/divide your gaming sensitivity)
2 ) In the same menu where you set your Windows sensitivity, you'll see a checked box titled "Enhance Pointer Precision" -> Uncheck it to disable it. Whether it fucks with accel or filters your mouse is up for debate, but it does fuck with your mouse.
3 ) Launch Steam, right-click on CS:S in Library, click Properties. Click Set Launch Options. Enter this, exactly:
-high -noforcemaccel -noforcemparms -noforcemspeed -nojoy
-high = Makes HL.EXE run at high cpu priority, which is good because cs:s is almost all cpu-based (so I've read/heard etc. yadda yadda)
-noforcemaccel = Disables mouse acceleration in CS:S (as opposed to manually editing config lines to achieve the same result. However, I have edited my config to disable mouse acceleration anyway so that's your call).
-noforcemparms = Ignores windows acceleration (hence, no need for CPL mousefix/fucking up your registry.
-noforcemspeed = Can't remember what it does :/ Try google.
-nojoy = Disables CS:S looking for a joystick when you launch it -> Saves memory (I know I know, we all have tons of memory anyway, but fuck it).
4 ) Adjust in-game sensitivity to your preference and you're done.
