I have installed Pc Lap Counter on Vista Ultimate and all is working.
I suggest to not install Pc Lap Counter in "C:\Program Files" because Vista will redirect some important files in another directory ("c:\Users\....") and that will cause some problem during a update of Pc Lap Counter version.
So on Vista is better to install Pc Lap Counter on the default directory (which is C:\Pc Lap Counter when installing on Vista).
You must
deactivate "the control of the user account" otherwise some component of PCLC can't work correctly.
Here is some print screen take from Pc Lap Counter on Vista: