I do want to point out that I have in fact read Toms Hardware's graphics card article, but I'm NOT technically inclined, and I think the cards listed are way over my head.

After the Xbox and the computer died in the same week, my husband and I have decided to consolidate and doing all gaming on the computer. We will be buying a new one, probably used or rebuilt, and I need to know what kind of graphics cards will best serve both of us. My husband likes shooter games like Half-Life and the like, but I play more casual games like The Sims 2 and City Life. Is there a card that can fill both of these needs? We are not hardcore gamers by any means, so we need little more than the bare minimum to run these games. Amazing 3-D grpahics are not that important, we just want the games to run decently, which they wouldn't on our old comuter.

The computer we are considering has an nvidia 8400 GS card - is that enough to run both or these kinds of games smoothly? If not, how much higher do we need to go for a mid-level experience?

I am not technically gifted - please explain in extreme layman's terms, if possible.

Thanks in advance for anyone with time to help out.

The 8400GS is not satisfactory for modern gaming. While it should run all of the games you've listed, if your husband likes newer shooters, like Call of Duty 4, Bioshock, Crysis, etc. it will not be able to run them. In this case, you should be looking for a 8600GT at a minimum, with a 8600GTS, HD3850, 8800GS, HD3870, 9600GT, or 8800GT being more favorable (in that order).