I need to manually add a 321x240@60 resolution in vmmaker for some non-MAME emulators (and because windows overrides my 320x240 with a fake 31khz one).
This shouldn't happen. Are you still using the patched drivers or trying with plain Catalyst?
I assume I just need to add the modeline to reslList.txt and rerun vmmaker? I know a modeline was posted around here somewhere but I can't seem to find it. I'm using the magic resolutions patch.
That won't work because x resolutions are rounded to 8 multiples by the modeline generator. Actually, the feature of using fake label numbers as 321, 322, etc. is reserved by the generator for the cases where it needs it (disambiguation of video modes with very close refresh rates), so you can't manually do it.
However, you can use Winmodelines to manually add that modeline. Make sure to use the 321 label for the numbers between quotations and that will do the trick.