[SWLUG] Matrox dual-head

[G Watkins]

Does anybody out there have dual displays working on a Red-Hat-type
system using a Matrox MGA450 or MGA550?
  I tried to configure things using Powerdesk, and for a while had
everything working so that I had one large desktop extending across both
screens. But attempts to configure so that I had a separate desktop on
each screen have led to the X-server crashing on start-up.
  If anyone has done this successfully, and made notes about it, I'd be
very grateful for a copy.

And a more basic question:
How can I stop the X-server repeatedly trying to start itself on
boot-up? (I looked for a likely process to kill but couldn't see one.)
Where (apart from one screen I saw when I first installed RH71) is the
configuration of whether to start in text or graphic mode?

I'd be grateful for any help.
Gareth Watkins