If you can run a cable from PC to the hifi, then job's a good 'un. Well worth doing. if you can't cable it up, then you'll need one of thos richer sounds boxes plugged in the hifi, with wirelass lan to the music on the PC, but I've not tried this myself.
For what it's worth, I bought a dedicated studio quality sound card for my PC (retails at £600+, though got mine much cheaper 2nd hand off fleabay), and though it is noticably better than the on board PC sound, it's by no means a "wow!" better. Comparison with both are played through proper hifi - Kef reference speakers, missioin amp blah blah - obviously played through hi fi is miles better than "computer" style speakers, never mind the built in sound.