Web conferencing/webinar tool recommendations needed

[Fekete Robert]

Dear List,

My company has decided to create web presentations about our software 
products, and I have won the assignment to find the right tool for the task.

I would be most interested in your experience with such tools, and any 
particular recommendations. I have summarized our requirements below:

The main goal is to bring our existing training materials online as 
presentations + live narratives from the instructor, with the attendees 
asking questions (text chat is Ok, but voice chat would be preferred).

- should be able to create interactive (chat) and non-interactive 
presentations from the same source if possible
- hosted on our local server if possible
- attendees should need only a web browser
- should run on Linux ("big names" like WebEx, Adobe Connect, or 
Netviewer seem to support only Windows)
- low-cost or open source solutions preferred, but other solutions 
welcome as well
- desktop sharing and whiteboarding not necessary, but nice-to-have

Thank you very much for your help.

Robert