Well you should definitely upgrade to 4GB of RAM and not just for D3 but because you just should.
I'm not terribly familiar with Radeon cards as I am Nvidia. I looked this one up though and it does seem a bit dated and you may have to turn some effects down in the game, possibly you'll have to run several things at medium settings.
I think the game recommends a quad core processor but I'd be more worried about your GPU. It's probably time for an upgrade.
I have a question regarding HDD's, and instead of creating a whole thread for it I thought it would be better to just post it in here. I'm currently in need of a new Hard-drive for my PC and was wondering if anyone knew of any good ones with nice RPM and internal/external transfer rates within a price range of 100$-250$.
Any help is greatly appreciated.
That's quite a difference in price. I could recommend a lot for 100 and a lot for 250. If you have 250 are you sure you don't wanna get an ssd? Gosh, they have lots of 120GB ssd's lately for about a dollar a gig. You could buy two of them! So if you more specific maybe I could help you more. Otherwise that would be my recommendation. But if you're set on getting an HDD, you also have a ton of options with that price range. And do you have SATA 3 on your mobo or not?
If it's just RPM stats you're looking for, they have those Velociraptors that are 10k RPM, and there are some other makes that even go as high as 15k RPM I think. But once you start getting that high of an RPM speed it really is better to consider an ssd or maybe even a hybrid which is what I'm currently using.