Compaq Deskpro 4000 series and text corruption

[Andrew Martin Adrian Cater <amacater@galactic.debian.org>]

Got Debian installed on the machines at work :)

X Windows runs fine: as does command line text mode _provided_
you boot from a rescue disk in single user mode or otherwise prevent 
X Windows from running.

Once X has run: the console is hosed:

scan            Text appears to overscan as the scan rate is set too high and
you also get m ss ng characters 
and $ prompts in the wrong place

X Server is the "old S3V": card is an embedded Compaq S3 Virge/GX

This is _apparently_ a common problem: no one else I know has managed to
get this working.  I want my six VT's back !!

Any clues ??

Andy