Humourous Fantasy Writers - Terry Pratchett
Terry Pratchett's home page
Terry Pratchett discussion forums
You can also check out the Terry Pratchett Usenet groups - alt.books.pratchett and alt.fan.pratchett. Terry himself posts on them from time to time. (I recommend a dedicated news reader like Thunderbird or XNews)
There's also a Terry Pratchett interview in issue 17 of Andromeda Spaceways Inflight Magazine.