Setting modelines, where

Debian, sarge, where do I tell the system which modelines it can use?

Background, I have the same monitor (LG 995E) on four different linux computers through a KVM switcher (no problems there). I am mostly talking about terminal windows here btw.

Boxen 1 is historic rh7.1 and xfonts (tvm?) are fine when I run x. Mostly it is a VT.
Boxen 2 is ex spud, ex woody, now sarge with gnome. Default X fonts were crap. but the cntrl &+/- allows a nice readable font to be selected.

boxen 3 & 4 have crap fonts. Using icewm, I have found that I can swap the default terminal font and choose another, but the screens still look crap on these boxen. It is like the monitor is out of focus.

So, I suspect that xdm/etc is using less than optimum modelines and I'd like to fiddle with the modelines so I determine if this is the problem.

I am not certain if it is a nVidia driver problem as I think I am just using the basic nv drivers on all boxen, without a recompiled kernel.

boxen 2 nVidia NV4 Riva TNT PCI
boxen 3 nVidia NV15 Geforce2 GTS AGP
boxen 4 nvidia NV5M64 Riva TNT2/64 AGP (same problem with S3virge driver & PCI card)

Reason for asking a 101 type question is that I am less than thrilled with crawling through the out of date doc that comes with Debian and trying to work out wtf they've done now.

Is it as simple as using gtf to generate modelines that you plug into the monitor section of XF86Config-4 and add a reference to the display modes under each depth of display?

I have tried this and the /var/log/XFree86.0.log shows the xdm(?) examinig a whole pile of "out of range" stuff before it even says "1024x768_85" is not defined.

Hoping to avoid the usual frustration.

TIA