Well I can open the files just fine, I guess the original poster doesn't have enough memory in his system to do so. but basically the problem is that the saved image has a resolution equal to whatever your WINDOW size is in the software.
I am now testing if reducing the window size would work fine. It did. I resized my window to 320x200 and DPIV recognized it as 320x200. It still thinks it's 256 colors though.
Here's what happens otherwise, the picture resolution is that of the window and not what you set as picture size on grafx2's options: