I don't believe so.
I have had conflicking Programs slowing my OS down.
I would not be cleaning the Registry.
Only absolutely necessary programs running in start up.
If your R.A.M. is set correctly,your Browser Cache empty,nothing odd showing in Event Viewer,
no site checking programs running,then it may be the No of programs installed.
A guru here may have another opinion, on what could be causing your slowness.:)