FPGA based VGA controller to drive PC monitor
Your monitor should auto-detect the resolution. You can eventually double-check this by hooking it to a PC with a VGA output, and force the screen resolution to 800x600. You'll see that the monitor will scale the image.

This scaling is done by the monitor, not by the video card. There is a "scaler chip" inside TFT monitors that takes care of that. More details can be found on the internet.