here comes the expert on recording
first to record using karaoke songs u need a multitrack recorder which on on track will play or song and on the other will record urs simltaneously so that u can hear and sing too. but such multitrack or even say some softwares (like karaoke island) dont come free. ofourse using softwares like adobe audition or soundforge(which r pros) give u much functionality in terms of editting ans mastering which karaoke island doesnt. see
*img204.imageshack.us/img204/620/kaho20na20kaho21xs.th.jpg
the image.
i have recorded my whistle using a karaoke song
u may try audacity. but im not sure if it allow karaoke recording