GTA IV is a demanding, CPU-bound game. So it would be better to tone down settings such as view- and detail distance and vehicle density to decrease the load on your processor. Set the the graphical settings to whatever you want- but try to be reasonable. While you are at it, set the resolution to 800x600, see what the resource usage is according to the in-game menu and save the settings.
Let's say the game estimates 500MB. You need to open the editor and create a new file called 'commandline' in the root folder of the game. That's how the content of it will look like:
-width <insert number>
-height <insert number>
-availablevidmem <insert value>
If the screen of your laptop has a resolution of, say, 1600x900, then -width is 1600 and -height is 900. In order to calculate the value you have to write after the -availablevidmem command line, devide the resource usage by the amount of VRAM your graphics-card has. That is 500/2048, in this case, which would be 0.244.