It almost sounds like you were trying to save a "scene file" or "model" from DAZ and open it into PS7...
Were you, in fact, trying to save an "image"? (in which case PS can open almost any image format you throw at it)

Granted, I haven't used DAZS in a few years, but when rendering out a still image you should have the capability to decide the image size and format - I suggest the largest you are wiling to work with (you can ALWAYS scale down, but scaling UP periodically proves to be problematic - wow, too many "p" words there...), and save it as a TIF so there's no compression and artifacting.

Good luck - hope that helps-
-Lew ;-)