Custom resolution

I have a RIVA TNT2 M64 card and I'm trying to support a PAL RGB
monitor under Windows2000; I need to set a 656x270 resolution at 50
Hz.
I was able to support the same monitor under Linux with the same card
modifying
the XF86Config modeline:

ModeLine "MyPALRGB" 13.5 656 702 756 864 270 284 286
312 +Vsync +Hsync

Whenever I try to add this custom resolution using the NVidia
configuration program , I get "The custom resolution input is
invalid".
I was able to set custom resolutions for different monitor (for
instance a 720x400@85Hz for a 16:9 monitor) but I haven't yet found a
way to set this one?

I remember I needed to modify the Linux driver in order to accept a
13.5Mhz dot clock; may be the case for the Windows driver too? In this
case there is no way to support the PAL RGB monitor unless modifying
the driver?

Thanks for the attention

Corrado Clementi