Reply: Commercial radio stations place a microphone close to each person, and feed all the mics into a mixer (ideally an automatic or gated mixer, which turns on only the mic of the person speaking). Typically the mics are ElectroVoice RE-20's or something similar.
If budget is a consideration, you could use a lower-cost mic on each person, such as a cardioid dynamic mic on a desk stand with a foam windscreen. Feed all the mics into a mixer.
An alternative is to have all the participants sit around a small table. Put a Crown PZM microphone on the table in the center. The Crown PZM-185 is the cheapest model but sounds a little trebly; the PZM-30D costs more but sounds natural. The PZM will pick up everyone around the table. To reduce the muddy sound from room reverberation, you need to add acoustic absorption to the studio room, such as acoustic foam, bass traps, fiberglass insulation covered with muslin (to contain the fibers), or curtains or moving blankets spaced about 1 foot from the walls.
If the room is acoustically dead, the PZM method works as well or better than several desk-stand mics, and costs far less.