Since I can't guarantee you guys own producing programs such as Acid PRO or Adobe Audition, I am going to teach you how to apply this trick using a free open-source audio editing program known as Audactiy.
Get Audacity. It is availible on all platforms and it is extremely lightweight. After you've installed Audacity, download the LAME mp3 encoder. You will need this to export your project as an mp3. Save it somewhere you will remember.
Drag and drop any mp3 into audacity. For this project, choose a song that contains normal vocals. So for all you Daft Punk fans out there, HBFS might not work, since those voices are barely human. For this, I chose Third Eye Blind's "Jumper." Listen to it now, so you can hear what the results were like when I finished applying the effect.
Third Eye Blind - Jumper [right click to download]
Now Let's Edit!
First off, you will need to split your stereo track into two separate channels. If you do not have two separate bars going across Audacity, your track is mono and this will not work. To separate into two channels, click the arrow next to the track title inside the gray box in your audio workspace. Select "Split Stereo."
Now, click anywhere on the gray box of the second channel. You will notice that that bar will darken slightly. Now select Effects -> Invert.
To finish up, select the drop down menu for each channel and select "Mono."
You're almost done! If you are happy with your results, just stop reading and enjoy. However, this next tip helps clean up the track and remove some noise and some residue left behind from the vocals. Hit Control+A (Command+A for Mac) to select all. Now, go to Effect->Amplify. In the box that appears, drag the cursor back to -5.0 db. Hit OK.
Now go back to Effect->Amplify and drag the cursor to +5.0db. What this trick does is remove all the lower-volume sounds, then boost up everything else back to normal. Again, this will not eliminate all the vocals, but it will make them extremely low volume if you hear them at all. When you sample these, you can always add effects to cover up whatever vocals are still present. Here are my results. The beginning sounds pretty weird, but the high pitched guitar was just too hard for Audacity to isolate. At around 1:00 is where you can see the best effect.
Third Eye Blind - Jumper (Prez Jordan's Instrumental) [right click to download]
Feel free to experiment with different songs to find which works best for you. I hope you got something out of this.