i5-560m dual core processor and NVIDIA GeForce GT 445M 3GB graphics card

Hello guys and gals (if there are any nerdy ones out there):

I have been looking at refurbed laptops and I was wondering whether the i5-560m dual core processor supports the nVidia GeForce 445m 3gb graphics card.  I keep noticing on the descriptions that it will list the 435m AND 445m graphics card, but the 435m will say with Optimus.  Does that mean that when it is not needed, it will use the Optimus with 1gb?  Or does it use the 445m graphics card w/o Optimus and utilize the 3gb always?  Doesn't the 3gb card use more power and would this mean that when it is not needed the Optimus kicks in and it uses less power?  Or would this just be another typo with the refurb website and it only comes with the 1gb 435m card?  A bit of an explanation would very much be appreciated as I've been doing a bunch of research the past couple weeks on buying a new laptop.

On another question, would it be smarter to buy the i5 processor instead of the quad core?  I do not plan to be overloading the laptop with applications and want it primarily for web browsing, light gaming, watching movies, and to begin music recording.  It is my understanding that since my use won't be too demanding, the dual core processor with a higher clock speed will be better than the multiple cores.  Or will the cache be more important?  Money isn't too much of a factor since the difference between the processors is only $200-$300 and I plan on paying it off over a year.  Will there be any performance differences between the two processors and the amount or type of RAM?  Like what is the difference between DDR3 and ECC?

And another quickie...  Windows 7 premium or ultimate?  What is the difference? 

thanks in advance for any help

jordan