I play everything in 1920x1200 with everything on ultra maximum... 640x480 was so voodoo 1 days... what was that? 13-14 years ago?
Get with the times! 1024x768 in my opinion is the current day standard minimum. Depending on the style of game you are making, this resolution may be excessive, but in most cases it's not. In fact, most of the games made by a large number of indie developers are, in my opinion, too low of a resolution. Why reduce something that could look awesome into a garble of barely recognisable pixels... especially this day in age.
If you can't run your game in at least 1024x768 then I'll send you the $15 it would cost to go buy a second hand graphics card capable of doing so.