Leo says to focus on areas he has interest, passion, and expertise. Content is king and making the best possible show is the best way to promote yourself. Once his show has quality content, he could try to get his show carried by a site like Machinima, which is the site his brother's content is on. It's important to understand that even the most popular internet celebrities aren't really making that much money. He should be doing it because he loves it, it's fun, and it's helping him achieve his goals.
In promoting the show and getting the word out, he should be active in the community he's podcasting about. Go to forums and contribute, but not spam them. He could put a link to his podcast in his signature, for example.
Ultimately in Tom's case, a bigger audience isn't what he necessarily should be shooting for. In new media, it's more important to build an active community than an audience.