asroc n68c-s ucc dual monitor conflict

[alhunter]

i am trying to get dual monitors connected. i select 256mb (others tried) in share memory option in bios and on reboot it locks up halfway throgh windows startup- sometimes with blue screen but mostly blank.
i am using an asus hd 5450 1gb ddr3 , 4gb main memory, windows xp 64bit, athlon x3 450 at 3.2ghz
i have installed all in one driver and asus drivers
either onboard graphics or asus graphics work but not together.
i have not got any over clocking activated- i have even tried reducing clock and mem speeds
any ideas?
thanks

[MarkJohnson]

You will probably need to install both monitors to your 5450. Your on-board is an nvidia graphics and you'll need to disable it, if it doesn't do it automatically. Not sure how well nvidia and ATI graphics can coexsist on same machine.

I take it, everything works with just one monitor connected?

-=Mark=-