I despise GarageBand for podcast work- much prefer Audition. It's a bit pricey, though.
You can use any host. If you have some experience with rss and such, you can choose to just have a standard web-host and do the work yourself, like I did. It's good to learn these things. Otherwise, there are solutions that will generate your RSS for you and such.
Also- it's PC only, but CastBlaster is nearing a full release and I hear it's pretty good.