There are many softwares that will allow you to edit, dub, and adjust the audio. There are free softwares where you can download 3 - 4 different programs to accomplish the task, there are consumer level programs (Ulead Studio, Ulead DVD Movie Factory), then are semi-pro level programs with more bells and whistles (Adobe Premiere Elements and Vegas Movie Studio), then there are the professional softwares (Adobe Premiere, Vegas 6 or 7, Avid Xpress, and others).
The consumer programs (ulead, etc), have wizards, and are pretty easy to learn and use, but offer limited levels of user control over the projects.
The free programs take a little time to learn (there are many guides/tutorials you and download which will help), and it takes multiple programs to accomplish the task.
You need to decide how much you will be doing this, and the level of control you want. More control generally corresponds to a better final product.