Dedicated Graphics memory means that the graphics has its own CPU running its own RAM to power the graphics acceleration. Shared Graphics memory takes RAM from the pool to power any graphic part of an application. I'll give you an example below
-lets say in order to run a video game, you need at least 700 MB system memory and depending on the settings of the graphics shaders or draw view distance (these are graphics properties along with game resolution) The higher they are, the more memory is required. So lets say it needs 400MB to run high graphics settings
1 GB Dedicated Graphics memory and you have 4GB RAM - The 400 MB will be taken from the dedicated graphics memory since it has 1 GB to spare. The remaining 700 MB will be taken from the 4GB RAM to run the program smoothly.
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2GB Shared Video Memory and 4GB ram - The 400 MB and the 700 MB are both taken from the 4GB ram since the 2GB "shared" video memory actually borrows it from the total system memory in order to run any graphics, so if you have a program or a game that uses 2GB of graphics to run (heaven forbid thats a graphic intensive program) you only have now 2 GB of RAM to spare. Now that 2GB is still needed to run BOTH the program and you operating system, your antivirus and whatever else is running in the background.
Do you get the concept?
DDR5 is definitely a higher choice vs DDR3 since it can power the data at a higher clockspeed or in a sense, more efficiently.
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I7 is definitely the gamer's choice for processor but for something that is not as graphic intensive (sims seems to be pretty forgiving on graphics cards.) processor does definitely help in the load times as well.
To be completely honest, personally, I wont spend over a thousand dollars on a laptop if I werent buying an Apple Mac. Since you are only using it to play Sims 3 and prolly light multitasking, you can get a decent macbook pro for $1.099 (you're a student right? so there's prolly a discount for you, ask an apple sales rep for it

) and you'll get more functions out of it and not have as much problems as you'll run into other windows based laptops.
Trust me, I was a windows advocate too, but crossing over, unless you are in a good budget, every tech guy will tell you to not overspend on a laptop (in this case over $1000) since I7's full potential isnt used yet, there is no software out there that developers have used its full processing power and people who do buy it are only getting it for heavy multitasking.
Save the extra money, go online and check how people optimize their laptops and be amazed at how a core 2 duo can have the same load times as a laptop that runs on I7 by default.