The trick isn't in changing the resolution in the FE. First you open it up in configuration mode while your desktop resolution is 1024X768. Then in your configuration in the frontend options, look for "resize" and set it to "true". This will make the FE match your desktop resolution. Now all you have to do is change your desktop resolution to 640X480 and... TADA!
However, fonts don't always appear as nicely so things may get a bit more difficult to read. After all, it was designed with 1024X768 in mind. Good luck.