1.Google "D3Dwindower" and download it from the first link which is fileplanet.
2.extract the files to a folder
3.run the program and click the plus icon
4.find gta3.exe in the folder where you installed the game, right click the shortcut for gta 3 and click open file location to find out where it's installed
5.while in the program, click on gta 3 and then settings which is the second to last icon
6.in the common tab click browse by DLL and select D3dHook.dll which will be in the folder where you extracted the program
7.in the common tab change the width and height to the resolution you want, the words are also reversed unless I'm stupid, the resolution that you set it to has to be the same or higher than the game, so you can't have the game run at 1600x900 in a 720x480 screen, its best to set it to the same for both
8.In the direct input tab check off cursor clip so your cursor doesn't go out of the game window
9.don't click the play/activate emulation icon or it won't work, just double click gta 3 inside the program to play
This took me a little while so if you can please reply if somethings wrong or it doesn't work for you.