Buy it. I have the same specs. I have to have pretty much all low settings (resolution at 1024 x 768) but it works fine for me.
It looks horrible compared to the consoles I guess but TBH, even apart from the mods, the command console ingame makes the PC version far superior, even with horrible graphics.
Oh, my settings are 1024 x 768, shadows off, water stuff set to low/off and I leave the rest at medium settings (when you start the launcher in options then you can select automatic settings: low, medium, high, ultra. I picked medium (what was suggested by the launcher itself for my hardware) and I just switched off all screen effects.
Actually, you might have to play at low settings but still, it works amazingly fine for me.
Though I've only played a few hours so far but I haven't had any stutter apart from with VATS, it can take up to 4 seconds just for the zoom in to happen. Apparently it's a known bug that was in Fallout 3 too but I never managed to find a fix for it.
Wait, I have a ATI 4200, but the 4250 is slightly better so logically it will work.