You will need some video editing software,
If your not going to add fancy logos and such then use Windows movie maker,
Alternatively you could use ulead video studio as a trial.
I bought it and it does a great job of editing.
Also for adding recorded voices use Audacity.
I use this as well,
Just record your voice and save as a wav then load the wav into the video editing software.
Heres one i done earlier :)
I used fraps, ulead video studio 10 and audacity.