The video goes from your computer to your screen via a VGA cable. Whats a VGA cable you ask? well look at the back of your monitor now and there should be two cables. Ones a power cable, the other is a VGA cable. Follow it back to the comp and see what plug it is, Thats a VGA cable and thats what youll be using.
For the cable for the audio, you want a 3.5mm to 2 rcas, go to the back of your comp again and find the sound card or onboard sound plugs. Chances are the cable coming out of this is a 3.5mm jack (same plug you have at the end of your headphones)
The other end should be 2 rca plugs, if not go buy yourself one of these cables, should cost like 5 bucks. So these 2 rcas hook straight up into your amp, simple!
see you over at aussiemagna