Heh.. sorry for the necromancy, though I happen to find it interesting this community is interested in podcasts as I've made some in the past (Thought not the kind of quality that could be put on this site...Some were.. howard stern level comedy.) and happen to extensively know the technical parts in producing them.
If you want the users to record audio on their own end it isn't bad(in fact it gives the best audio quality), but can be frustrating to edit all those streams, specially if they don't know alot about recording audio which can result in off synced audio or wrong speed rates, or they could simply forget..Frustrating none the less.
Alternatives which are more common among the podcasts communities is usually these methods
Softwear approach
Skype:A key runner in Podcast development, it's fairly popular, if you want phones the unlimited service is cheap and it supports an massive amount of callers, listeners, and most importantly plugins. Currently I personally use "Skype call recorder" its a free program that isn't that bad, specially since it allows you to record in split stereo having the host on one channel while the rest are on the other for editing purposes.
Advantage:Easy to set up, usually 1 button record with a mp3 file that can be around 1 or 2 mb per minute.
Disadvantage:Audio quality can be slightly lower in using these sort of programs but most podcast listeners wouldn't notice or care.
Hardware approach:
Two computers or a Computer and recording device
The method essentially has a user use a recording softwear like Audacity, while either using a separate stereo channel on the soundcard (Or a Y splitter with a double ended audio cable) to another computer or recording device. There are advantages and disadvantages to this set up.
Advantaged:Better audio quality, but not as good as recording from the people on their own.
Disadvantage:Syncing the audio, open to "failures" if someone forgets to push a button.Requiring two monitors, requiring a better soundcard if your using a laptop since laptop soundcards are junk.
Just remember.. the old radio saying "The man with the tape recorder has the best voice", this will be true in ALL cases.
Ofcourse hardware wise you could also bring in audio mixers and other fun things, but I'm trying to keep it at basics for now.
Editing wise, Audacity is the most popular choice as it's filled with plugins and features.
Now the "Cast" part of Podcast is a bit more troublesome.
Podcasts are normally done with a RSS feed, and need to be hosted on a website with some good bandwidth. Alternatively you could stream the audio off websites like Imeem.com or Podcast streaming sites like
www.podtrac.com This would help as if your doing more then 30 minute long shows it can lead into 50 mb or more file sizes, this can eat bandwidth quick if your show is popular. Not to mention storage requirements for archives. Well.. you can supplement your bandwidth with websites like
http://www.cachefly.com/ and such..but thats only if your stuff is really popular.
Anyway.. that's my two cents. Everything else is just basics like do soundchecks, be ready for failures, make sure to always use headsets and microphones or telephones since you get feedback and echos and all that.