|Ok, I don't usually answer a question with a question but this time I have to.|
You asked, "we would like to know the possibilities of video conferencing over LAN."
My question is, since you're asking about videconferencing on a LAN I have to wonder why you wouldn't all just get together in a meeting room and talk face-to-face. Using a videoconference within an office environment just makes no sense considering the effort required.
To answer your question, sure it's possible. All you'd require is some kind of chat software that will support the number of users you have who will be participating and will work over a LAN. As to what software, I can't say. But if it was me looking, I'd start by using google.
I will add, wireless is not a medium I would consider using for videoconferencing. Considering it's inherent issues, I think you'd be lucky to get it working smoothly.