Hi,
follow this link:
http://zone.ni.com/devzone/explprog.nsf/webmain/EBF11DD1F0FEAEF3862566790072A983?opendocument&node=DZ53008_US
You will get a lot of useful functions.
In the Winsys.llb you find Get Screen Size.vi that returns the screen resolution.
Good luck,
Alberto