I'm in the process of buying a new computer and am not interested in a kit build or the like, as such, I'm stuck with a pre determined GPU.
The comp's mainly to be used for older games, stuff from 2004 and earlier, MUDding, which requires nothing in terms of GPU power, HD movies without latency would be nice for a change, but also with the option to possibly run newer games at decent visuals should something good show up, which seems unlikely with games these days.
The GPU options are an Nvidia 260 GTX, which judging by the charts really doesn't seem that amazing. With 1,8 gigs of mem. Comes with a quad core computer.
240 GTS, again with a quad core.
230 GT, quad core. Don't have any info on this card at all. Possibly a rebranded 220 GT OEM?
Or finally, an ATI HD 5450, that comes with a dual core i3. Not too sold on this one, although the i3 is just about all I'd need. The 64 bit bus seems like a joke considering cards almost 10 years old were already sporting 128 bits. But the lack of a fan would be a nice change from the loud one from the 7600 GT I've been using over the years.
If I were to buy a new card, I'd most likely have to buy a new PSU too as manufacturers never seem to pick even a half decent PSU for their ready made computers. But yeah, those are the choices, and I'm not immediately looking to buy a new card either.
Well the GTX 260 is the only one you listed that is a real gaming card capable of handling modern games at a respectable resolution. In general though I recommend just ignoring the video card and focusing on getting the computer you want for the right price. It's usually cheaper to just buy something with a cheap low end card and then buy a gaming card separately. However if you are really only interested in games over 5 years old then any of those will do, or even just putting in your old 7600GT. If you do end up wanting to replace the card the HD5670 is a good choice that isn't too expensive($90), will work on anything but extremely weak power supplies and can handle current games at modest resolutions like 1280x1024 and below. For something better that's also a good buy($150) there's the HD5770 which is pretty nice even at high resolution like 1920x1080.