This is a key feature of Wirecast. I don't think Telestream pushes this enough.
With Wirecast you can download any number of Desktop Presenters for both Mac and Windows (it's free). So in other words you can have several Mac and Windows PCs on the LAN and they'll ALL send to Wirecast regardless of whether Wirecast is running on Mac or Windows. You can sent the entire desktop or select a specific window of a specific program. Since it's all coming to you over LAN (make sure you have good bandwidth) you're not tying up any video inputs with converters.
One of my favorite tricks on the Mac side is to use DTP on the same computer as Wirecast and take Skype Video calls and send the video to Wirecast with DTP and the audio with SoundFlower so I can do one on one interviews with guests who Skype Video in.
Craig, I have a question about taking skype on the same computer as wirecast. First, do you need a second monitor attached so Wirecast is off of the DTP desktop area and second, if you send the audio to soundflower, how can you hear it.
I have a slightly different need. Second laptop using skype with laptop audio so audience can hear it. I will be broafdcasting to ustream so I need skype audio. I thought of doing:
1. Have skyper connect with other laptop AND me at the same time. (can skype do that) The other computer will share audio to the crowd. I have second monitor on my MBP. I add the wirecast interface to other monitor and have skype on my main laptop monitor with video via DTP and audio to soundflower