my airport has two non parllel non intersecting runways, they make an angle of about 13deg.Can I make fsx use them simultaneously? and specify which one's only for takeoff, etc?

Yes, but right now there is no good graphical tool which can do that like AFCAD in FS2004. You have to modify the XML code.Which airport?I'm working on a FSX version of the tutorial.Sounds like a good example.

I am working on VIDP.What do I need to modify in the XML?

Can the runway usage be made time dependent also? Most airports have specific time periods when they daily shutdown/switch runways for maintenance.