Which version of Photoshop are you running? Adobe Camera Raw is a free plugin for photoshop but not all versions of ACR will run with all versions of photoshop. Strangely enough, ACR V3.x doesn't work with CS, but does work with elements 3 or higher! I find it works very quickly with my Athlon 3200 and 1GB RAM.
Duncan.
Some more info here:
http://www.adobe.com/products/photoshop/cameraraw.html