Dedicated graphics card

[slimkiller]

If a laptop has a dedicated graphics card, can I replace the graphics card or the processor without having to replace both at the same time?

Im specifically talking about the ASUS G51J-a1 laptop if it depends on the laptop itself:

http://www.newegg.com/Product/Product.aspx?Item=N82E16834220605&Tpk=g51j-a1

And are there any 15'6 or 16 inch laptops with dual graphic cards?

 

[Maziar]

First of all upgrading a part by yourself voids the warranty,about the G51J,you can upgrade the CPU to a faster i7 model if you want.
And about your second question,the answer is no and its because of the heat,some laptops with 17-18.4" have dual graphic cards like AW M17x and Sager NP9850