Command line arguments

You can indeed add some intersting command line arguments when starting GTA4. The list of arguments is found in the readme file in the install dir of GTA4 or here.
You can now define your graphics resolution and parameters as well as start in windowed mode.
Just add them to the GTALauncher call. For example: In order to set maximal details indented of the available video memory you need to extend the shortcut targeted at the "GTA4Launcher.exe” with the parameters "-norestrictions" and "-nomemrestrict".
Another option should be to create a file commandline.txt and put them there. Has to be placed in the install directory (not tested that myself yet).