2 mics for one podcast

Let's assume for a moment that they are indeed both USB... there's no way that the digitising clocks in them can be synchronised, so no normal driver is going to be able to cope with them, as the output from one needs to be synchronous with the first one in order for both of them to be recorded. Is there a fix for this? The only one I'm aware of is ASIO4ALL, which you will find at http://www.asio4all.org/, which allows one source to be resampled so that its clock aligns with the other one. Will this resampling affect the quality? Yes it will, but you might find that you're able to cope with this - it depends on you, and how bad you think the resampling sounds.

The good news is that ASIO4ALL is free, and also gives you better diagnostics than any of Audition's drivers; it will tell you quite clearly whether both devices are available.

The ideal solution to more guests though isn't USB mics, but 'normal' mics and a mixer - you don't have these difficulties then.