I don't believe that exists. Can you post a link to the specs? My guess is that the CPU is 2.6GHz. (edit: It is actually Intel Core i7 720QM @ 1.60GHz, I assume a mobile version of the core i7 at 45w.)

It isn't "better". DDR3 is capable of higher speeds and higher densities than DDR2, just like DDR2 was capable of higher speeds/densities than DDR, etc, etc. Initially the higher speed memory will just add more wait states, so it ends up being equivalent speeds, but DDR3 has room to get faster/bigger, DDR2 doesn't. Everybody is moving to DDR3 and the price points have already crossed, so DDR2 will be moving towards obsolete soon. You will be able to buy DDR2 for years, but DDR3 will be/is the mainstream technology and in the computer biz, the mainstream technology becomes the most cost effective solution for everybody. As far as I know, the price points have already crossed, so there's no price penalty for going with DDR3 now, and there may even be a slight price advantage.

If you buy a system with core 2 duo or quad, you will probably get a system with DDR2, and there's nothing wrong with that. Those systems are still very capable today. If you buy a system around a core i5 or i7, you will probably get DDR3 with that system.

No, you don't need it unless there's a feature it has that you seriously need. For most people Windows 7 Home Premium is fully capable of doing workgroups and everything else. Some people might benefit from the Pro version, but most of us don't need it.