What VGA cart you have than?
I did do it in the past myself as well i needed it to change my monitor vor the ECAM screens 90 degrees and it did worked fine for me...
I am not sure anymore what cart it was but or ATI or NVIDIA both can do the same it is mention in the advance options of your monitors..when you install that extra software that you can download on there site.
gr.
Frans M
www.airbus320.nl