1) Copy this to your userlibs folder:
http://www.blitzbasic.com/codearcs/codearcs.php?code=1179
2) Use the following code anywhere after 'Graphics' or 'Graphics3D' to set the window's position and size (replacing x, y, w, and h with your own values). Don't exceed the window size that you set with the Graphics command though or it will probably mess up.
EDIT: This won't affect the small startup window but there's a hack which allows you to get rid of that completely. Then you can change the size of the main window as and when you please.
http://www.blitzbasic.com/codearcs/codearcs.php?code=1179
2) Use the following code anywhere after 'Graphics' or 'Graphics3D' to set the window's position and size (replacing x, y, w, and h with your own values). Don't exceed the window size that you set with the Graphics command though or it will probably mess up.
hWnd=SystemProperty("apphWnd") api_SetWindowPos hWnd,0,x,y,w,h,0
EDIT: This won't affect the small startup window but there's a hack which allows you to get rid of that completely. Then you can change the size of the main window as and when you please.