Hello Jerry, welcome to the forum.
Unfortunately you will have to upgrade to photoshop CS4 if you want to continue editing your RAW files through photoshop. CS2's bridge will not open RAW files from newer cameras. You'd have to convert the files to DNG or open them up in Nikon NX View (free program) or Capture NX2 (pricey) and then open in CS2 as TIFF files. I believe support for CS2 RAW files ended with Nikon's D200/D80 or thereabouts.
Lightroom is a cheaper alternative if all your going to be doing is editing your photos. However since your using a Mac computer then it's out of the question as it runs only on PCs. Aperture is a great alternative to Lightroom. Capture One 4Pro is OK, but it's expensive and is geared more towards professionals. Nikon Capture NX2 is the best at manipulating your Nikon pixels but it is very buggy and tends to do weird things sometimes. It's also the slowest at rendering files too.
If cost is an issue you can convert your RAW files using NXview (free) make adjustments to the RAW file and saving your files as TIFFs. You can then open the files in CS2 work on them further and save as PSD files. Lots of extra steps so it's time consuming but the cheapest alternative. Otherwise you will have to spend money on new software. Though all these programs will take time to learn if you are not familiar with them.
Nikon Capture NX2 was only free with a D300 purchase for a limited time when it was first introduced.