sound forge 8 dosn't seem to be desingned for removing vocals, i saw some free (demo) software specificaly designed for that purpoe, but I would be suprised if the abouve people were wrong, you might wan't to try recording your own voice on a seperate track, and the reverse the polarity (sorry I don't know a "simpler" term for that, it's cinda like flipping the track "upside down" cancalling out the "right side up version" <note this is not a definition, but a real definition is even more confusing) in hopes of canceling it out
but you would have to sing exsacly the same as the original voice to do so, and i'm still not shure if that would work (i have never tried it, i know it works for getting rid of a click track that might have bled true the headphones) but since i hate taking other people's work i heve never tried it before with vocals