Question: I have to sync iCal on all the computers without having a MobileMe account, I would like it to be "live" because the co-workers have to see the changes right away on their screens, they also need to be able to edit and stay sync on the rest of the LAN.

There isn't a server available - so a server solution such as iCal Server won't work.

Answer: 
Use [Google Calendar + CalDav](http://www.google.com/support/calendar/bin/answer.py?hl=en&answer=99358#ical).

We use it as our calendar for our business, and it's solid. iCal integration is not 100% (no tasks, each calendar is a new account), but the most important parts are even better than iCal Server IMO. Having google email or SMS you a few hours before a meeting is especially nice.
Check out [Zimbra Open Source Edition](http://www.zimbra.com/community/downloads.html). It supports CalDAV for Leopard clients as well as address book Sync. You won't need to setup a dedicated server since it supports Mac OSX as a server platform or you could run it under a Linux virtual machine with VirtualBox/VMWare Fusion/Parallels and make it portable.