So any game that has a res greater than 256 lines on the vertical will always have overscan?
Sure.
Is there a way i can 'trick' groovymame into display these game so that fit into my display without having to alter the vertical adjust through the TV service menu??
Yes, you can change this value (active lines limit), so that anything above 256 will be interlaced + stretched
15625-16200, 49.50-65.00, 3.500, 4.7000, 9.500, 0.064, 0.260, 1.200, 0, 0,
256, 448
but what values do i have to write down for the monitor_specs line, and surely if ive only edited a few video resolutions how is this changing/altering the monitor_spec line within the mame.ini file?
It's very easy, once you have a resolution centered, go both into horizontal and vertical geometry submenus. You'll see the values you need on the right of each line, so:
H Front porch
H Sync pulse
H Back porch
... correspond with these ones (same order):
15625-16200, 49.50-65.00,
3.500, 4.7000, 9.500, 0.064, 0.260, 1.200, 0, 0, 256, 448
... same for vertical values:
15625-16200, 49.50-65.00, 3.500, 4.7000, 9.500,
0.064, 0.260, 1.200, 0, 0, 256, 448
So the meaning of all this is not to center a particular resolution (that is overriden anyway by GroovyMAME).
What we do is to ensure that all the modelines recalculated from that monitor_specs line are similar to the one you just centered with Arcade_OSD (which values you've obtained).
maybe a guide is in need for using Arcade_OSD correctly?
Definitely, you'll probably have some news soon.