Thank you, anyways, i just discovered how to do it using only blitz3d, just including two graphics commands:
Graphics 800,600,16,2
Graphics 640,480,16,3
SetBuffer BackBuffer()
Doing it makes the scalable window to be created in 800*600
Graphics 800,600,16,2
Graphics 640,480,16,3
SetBuffer BackBuffer()
Doing it makes the scalable window to be created in 800*600