To do a let's play first you would need
.Fraps registered version
An unregistered version sucks because it would need 37 dollars just for that
.Audacity
It's totally free
.Microphone/Webcam and Skype
Mic and Webcam probably is expensive so...there is no other choice and Skype is only when you want to play with anyone else
I could do the recording, skype, and use Audacity because I already have all things needed