The podcast author and episode artist fields come from the <itunes:author> tag in the XML feed file. You might look through the options you have available in garage band and iWeb.
Here's an example episode <item> tag from the iTunes podcast tech spec
http://www.apple.com/itunes/store/podcaststechspecs.html#example
<item>
<title>Shake Shake Shake Your Spices</title>
<itunes:author>John Doe</itunes:author>
<itunes:subtitle>A short primer on table spices</itunes:subtitle>
<itunes:summary>This week we talk about salt and pepper shakers, comparing and contrasting pour rates, construction materials, and overall aesthetics. Come and join the party!</itunes:summary>
<enclosure url="http://example.com/podcasts/everything/AllAboutEverythingEpisode3.m4a" length="8727310" type="audio/x-m4a" />
<guid>
http://example.com/podcasts/archive/aae20050615.m4a</guid>
<pubDate>Wed, 15 Jun 2005 19:00:00 GMT</pubDate>
<itunes:duration>7:04</itunes:duration>
<itunes:keywords>salt, pepper, shaker, exciting</itunes:keywords>
</item>
In this case "John Doe" would show up in the artist column for this podcast episode.
Erik