yes you can lisson to music from your computer on your hifi.you may need a sound card or on board sound with line out and a 1/8 stereo to rca duel connectors. and a couple of double ended rca cables to go from those to hifi line in.
next you will need a tv card for your computer.
you have tiger direct now in uk have a look in there site for what you need. there are many others sites to look at allso.