What I did was start commentating on a match that was on TV, it is much more natural that way (which will best show your talent). Just plug a microphone in to your PC and then use some sound recording software (I would recommend Audacity) to get it recorded. Then save it as something that isn't a WAV file. A simple way is to import it into iTunes and then right click on it in the library and click Convert Selection to ..., where ... is either AAC or MP3, it shouldn't matter which at this stage. Audacity has built in options for saving as OGG (which will play in VLC) and you can get plugins to make it save as MP3. No one wants to download 100mb for a few minutes of you talking and it might harm your chances.How will people audition? By reciting a few lines? And how will it be recorded?
Something else I'd like to mention, this isn't for 'putting on' accents, speak in your natural voice.