I used to work as a Gateway technician when the 500 series came out last year. Looking at the current line they haven't changed the case configuration so I can say the PSU's are the normal ATX shape and connectors are compatable but the case has *no* PSU screws in the back and uses a tool less lever lock system:
I think the 700 series use 200W+ PSU's that will fit in the 500 case or you can mod a 3rd party one in with alittle ingenuity. (beware GW charges a arm+leg for parts) Now the case itself has a plastic shell over metal frame, and a thick flip down door for the cdrom bays so it is pretty quiet. This should be the case
being used for the current 500 series or something very close to it. And this should be
the same or simular to the PSU that goes with it.From my experience the use a 160W PSU's worked perfectly fine with the stock configuration and any addon configurations that GW offer to upgrade it too. The 60mm cpu fan was defintely the loudest item in the system and I would not hesitate to swap that out if you do buy one. The PSU is okay as far as I could tell listening to it in the noisy shop environment I worked in (note: it uses a 80mm screw mounted under the PSU blowing up config which does dull the noise some)
As a counterpoint, several of my friends have picked up Dell Dimensions recently and the one thing I like about their design that make them quiet for a off-the-shelf system is the use of a quiet rear mounted NMB brand 92mm fan and a *duct* to suck air off the cpu. You can sort see what I mean here
but you can't see the fan inside the rear housing. The fan is spaced away some from the rear grills (which are quite aerodynamic).Team that with a plastic shelled case and Seagate drives (my friends came built with them, YMMV) and they are nice quiet systems. The PSU's used 80mm NMB fans blowing directly out the back, but they seem to be wired quiet since they don't have to vent CPU heat.