first up is audacity try this link to download it

http://audacity.sourceforge.net/download… Just click the installer & the download will start.

second is Sony Vegas 7 & its also free & its a video editor as well, you can get its registration key by searching

http://www.sonycreativesoftware.com/dl/d…

& then third is Gold Wave its also free

http://download.cnet.com/GoldWave/3000-2…

try these links to learn how to use these in this situation

this is for audacity tutorial

http://www.youtube.com/watch?v=PqXiKYG3J…

this is for sony vegas 7

http://www.youtube.com/watch?v=6AN8Ch2OC…

this for gold wave

http://www.youtube.com/watch?v=twGPOPSRq…

now after removing vocals of your band try this software

http://www.nchsoftware.com/videopad/index.html

in video pad drag your recording then just drag the other your band’s recording(without vocals)
& then add your singing on the top sound bar or space or section where a grey line is being displayed & then right click your band’s song & click move track to & select track 2 then adjust them so they end in the same time line & then click save & you have your favorite band’s song with your sound of vocals.

if my answer works then please select it as best & give me a thumbs up.