I had to reinstall Steam recently and i noticed they have changed the directory for steam. It is now progfiles/valve/steam not progfiles/steam therefore when going to install v3b1 (necessary for v3b4 and v3b4a) it doesnt even let you choose your own game dir, it just automaticaly extracts to progfiles/steam/halflife/nsp therefore making a whole new directory with not a single steam file in it. I find this will pose as a bigger problem for newbies or people that dont know how to copy and past the directory. NS should fix this immediately and let you choose your own path rather than having to copy and paste the ns directory into the correct steam folder.

IIRC, the installer reads the Steam folder from your registry. Your registry is obviously telling NS the location of your old Steam install. Perhaps you should fix this.

Or do some folder moving.