HOW CAN I HOOK THE Panasonic TH-42PX75U TO THE VGA OUTPUT ON MY COMPUTER?

If your computer has an HDMI socket, all you need is an HDMI cable. If not you need a VGA cable (the blue cable that usually connects a computer to it's monitor. One end goes into the socket on your TV marked VGA or PC. the other end goes into the monitor output on your computer. if you have a laptop, there will be a vga socket (usually blue inlay in the socket) on the side or back. you will then need to set up the second screen in Control panel, display settings. If using the VGA cable, you will need to run an audio cable from the speaker/headphone socket of your computer to your tv (there will be a 3.5mm jack near the VGA socket) or to your audio receiver.
Good luck.