Sufyan: As a former user of a laptop with the R300 chipset, I can only agree with voodoo47 that the GPU is the bottle neck. It was ridiculously underperforming in anything more straining than video playback, I think it would struggle with SS2 even under the original Dark engine, and I'm not surprised to hear that you're having issues with the NewDark engine. By the way, that fact makes it less of an old game: Don't let old looking art assets deceive you, the NewDark engine is up to specs for Windows Vista and beyond. The game you are playing now is not the same you would have found of an original print disc.
I know, but without the SS2Tool, it's the old game without the NewDark engine and it runs fine on my system (60 FPS).
I also tried the tool without multisampling a couple of minutes ago, but nothing happened in terms of improved perfomance.
I'll go vanilla for the time being and i'll use the tool and mods whenever i'll get my new PC.
Anyway, thanks everyone for the help.