I certainly wouldn't recommend using speaker outputs to feed a PC audio input. Placing an incorrect impedance across the hifi speaker output could damage its amplifier circuit. Also, unless great care was taken to keep the hifi volume to an absolute minimum, there's a significant risk of damage to the PC circuitry.
A much better solution would be to use the headphones socket from the hifi. Keep the hifi volume set fairly low and listen to the output, while recording, through the PC's speakers. Hifi purists will point out that this method isn't perfect but I've used it myself with good results. Your local branch of Maplins can supply a suitable cable.
Chris