+1 for Audacity, especially seeing what you want it for.
You will want a better mic, than a standard "computer mic" for what you want to do, also. Standard "PA" type mics will not work or will have a very low volume level connected directly to a PC sound card. You will need a mixer or some other preamp to bring the PA mic's volume level up to near line level for the PC. An alternate is a "better grade" USB mic.