well, since your not a gamer the heatsink version might work okay. assuming you aren't building your own 3d models or anything
The thing is without active cooling, things could get heated. Not saying don't get one, just be aware of the issue beforehand. What card are you looking at exactly? how many cd/dvd/harddrives are you running?
And yes, getting a video card would smooth things out. not only will it use its own vram to render but will let your OS/programs use the full gig of regular RAM you have in there.
Personally, I would get a small but ample PSU 400ish and like a 73-7600 nVidia card. probly get both for about 75 bucks or so.