Last night I set up my Nikon Super Coolscan 4000 ED film scanner with my Mac Mini. As the Mac already had Adobe Photoshop CS2 installed, I expected Nikon Scan 4 to install a plug-in (as Nikon Scan 3.1.4 had with Adobe Photoshop 7 under Windows XP) but this was not the case (it had worked previously for my Canon CanoScan N656U flatbed scanner).
After contacting the Nikon European customer support desk (who in my experience are always helpful), I copied the Nikon Scan Plugin 4 file from Applications > Nikon Software > Nikon Scan 4 > Plug-ins to Applications > Adobe Photoshop CS2 > Plug-Ins > Import/Export. Now Photoshop CS2 has a Nikon Scan 4 entry under File > Import, allowing me to scan directly to Photoshop.