I wanted to add a sound clip from a DVD movie to one of my own clips and then post the edited clip on my homepage so I need to know before I proceed if this would be considered copyright infringement?
Yes, copying and publishing someone else's copyrighted materials could be an infringement, especially if the primary purpose is for your own convenience or profit (which would undermine the defense of "fair use"). However, if the "clip" is not a substantial or recognizable portion of any particular DVD soundtrack, it may be difficult for the owners to prove that it infringes or causes them any harm. A professional would go ahead and obtain a license before using someone else's works for profit, or else make a new performance (cover) of the same music and file for a mandatory mechanical license. This assumes the music is copyrighted and the sound recording of it is also covered by copyright or something similar.