What recommendations do you have for a technology that allows me to conduct a Webcast (basically share a Webcam) with up to 500 people concurrently?

If the technology belongs to you, attempt to patent. Then approach two or three companies in your market that would be customers. Run a six to nine month pilot. Collect feedback and testimonials regarding the product use. Now identify current competitors in the market to either sell the technology or lease it. If you decide to go the start-up route, it is not impossible but very hard as there are established names in this space. Regardless of the direction you chose, without live customer feedback you only have an unproven concept.
Goodluck.

I think you are asking what tools to use to host a webinar type of event. There are a couple good ones to pick from.

Low Budget: http://www.freeteleconference.com/
Gives you the ability to record and replay at will. Use GoTo Meeting for the slides and voice over IP. Free Teleconference may allow you to provide a call in phone number also.

Higher Budget/Full Featured:
www.infusionsoft.com