I'm willing to bet your system will run the game just fine.
Most systems will lag with a very large fleet when zooming in onto them, even with 256 RAM graphics cards.
I have a Dell Vostro 1000 with 1Gb of RAM and 128 mb of graphics. Yes, the card is also integrated. SINS works fine on my system, with the settings being on high, and ship details on "highest". Game runs without any lag, but once the map gets big (over 60 planets) or I zoom in on a very large fleet, the game will lag. However, it's never been unplayable. It's been on the edge of unplayable only once though, and that was when I was playing a 5 star system with over 100 planets (I think I picked the biggest map available)... The reason that such a new game is more friendly to old systems is that the game does not display the same amount of graphical effects as for example a first-person shooter would. In such games, the entire vicinity moves, but in SINS, the only things are ships and planets, the background is just a very large desktop background to put it like that.
However, this all changes when taking in account what kind of OS you are running. If you are runing XP, your 4 Gb's of RAM will laugh at the game, but if you are running Vista, things get different. I am running XP...
Go get the game, my system is at least 2 years old, yours will be running this without any problem. But just to be sure, try to get your hands on a demo first to see if you like the game 
