Well first of all welcome

And to address your issue, to me it seems your graphics card is holding you back.
Your CPU or RAM shouldn't cause you the graphics problems; I've got a five year old AMD 2 Ghz CPU (but not dual core as yours) + 2 Gig Ram like you and my sh3 runs fine.
But a graphics card with less than 512mb might have a pretty hard time running sh3.
HOWEVER I almost immediately started playing with GWX, and I really can't remember what stock sh3 really looked like graphics-wise. (By that I mean, for all I know, your screenshots look just like STOCK sh3 would look, but -as far as I can tell- nobody here plays sh3 without a mod that makes it look better

)
GWX makes the game look a lot better without putting too much strain on your computer, so the first thing I would recommend is: install GWX!! Seriously, you miss out on a lot when you just run sh3 stock. These guys made the game so much better UBI should have offered them full time jobs. (And it's not just graphics, it's a complete overhaul of game mechanics, units, realism; you name it, it's there) + there are other super-mods too, like NYGM or the upcoming HAHD-mod. Check out
http://www.u-boot-hahd.com/ubootwebsite/ I'm not even spamming, I got nothing to do with it, but those guys are really in the process of creating a jewel.
To sum it up, the weird thing is; you'll probably never are going to run into a game that you can adapt to your own taste like SH3. Now I only mentioned the huge mods, but there are dozens, if not hundreds of more little mods that really enhance the game. Just search the forum or the downloads section.
btw, if you can tweak your graphics card settings as you said, anti-aliasing might be worth a try to make it look more smooth; but it can also mean your FPS will plummet below freezing point

Just a trial end error kinda thing.