Graphics card and new monitor or a plug & play problem

I have just got a HP LP 2465 monitor and plugged it into the DVI port on my
Radeon 9200 SE graphics card installed in an Evesham machine (MSI AMD NVIDIA
Force 2IGP motherboard with a 250 W PSU) along side an AOC VDU plugged into
the VGA port. Around 50% of the time on boot up, it will fail to recognise
the HP screen and install another driver / colour monitor profile. I have
increased the PSU to 300 W which did improve the behaviour of the display on
the AOC (it showed the full screen rather than just part of it) but did not
solve the unreliability of the system. HP says the monitor will work
provided it is connected to a card which can provide 1920 x 1200 pixels at 60
Hz, which the card can and does achieve (for some of the time).

I have installed up to date drivers, updated the BIOS and disabled the
motherboard's graphics card. I have rebuilt the software from a reformatted
hard drive to minimise driver conflicts.

I speculate that the plug and play during XP start up is not able to
recognise the monitor, possibly it may still be having trouble with power to
the card (given its supply is routed via the mother board). Can any one
confirm this hypothesis or suggest a solution (other than a new motherboard
etc etc)? In particular, I was wondering if one could force plug and play
to select only one choice at start up?

Many thanks in anticipation