Wikipedia's article on EDID talks about the "divide by 8" issue, specifically in reference to this resolution:
http://en.wikipedia.org/wiki/Extended_display_identification_data#Limitations
A replacement VGA cable isn't going to do anything. (A bad VGA cable is the suspect is if all a monitor will do is something *really* least common denominator like 640x480 or 800x600. You're getting "close to the right resolution", which indicates it's reading the data channel and interpreting the best it can.) More Googling suggests that older ATI cards in particular have problems with non-divisible-by-8 resolutions, up to not being able to do them *at all*, at least out their VGA ports.
Unfortunately I suspect Osgeld is probably right and you may really be stuffed. Does the monitor have a DVI port, and to you have a DVI equipped machine you could try it on? That might be the only chance you have.
http://en.wikipedia.org/wiki/Extended_display_identification_data#Limitations
A replacement VGA cable isn't going to do anything. (A bad VGA cable is the suspect is if all a monitor will do is something *really* least common denominator like 640x480 or 800x600. You're getting "close to the right resolution", which indicates it's reading the data channel and interpreting the best it can.) More Googling suggests that older ATI cards in particular have problems with non-divisible-by-8 resolutions, up to not being able to do them *at all*, at least out their VGA ports.
Unfortunately I suspect Osgeld is probably right and you may really be stuffed. Does the monitor have a DVI port, and to you have a DVI equipped machine you could try it on? That might be the only chance you have.