Not possible.

A document management system is a must for that many documents. Check out Alfresco. It's open source and as such isn't outrageously expensive like it's competitors. If setup seems too daunting for you, check out tsgrp.com. Technology Services Group is a consulting firm in Chicago with experience working with Alfresco and may be able to make this transition easier for you.

I want someone from Lenovo to tell me honestly that they believe that a Lenovo computer I buy from them will be ready for me to use in the way most people expect to use their computers when it comes out of the box. I want them to tell me that it will be secure, that it will be free of garbage-ware, and that it will have the most commonly used programs pre-installed. They can't do that. When Dell sells me a computer preloaded with Ubuntu, they can.

Echoing what tbuskey said, it does seem as though you should already have something in place that blocks nonessential outgoing ports (firewall) and if you really do have as strict of requirements as you say, something like an 8e6 device that blocks outgoing access to undesirable servers running on ports 80 and 443. If this is the case, you should have no trouble keeping your users from connecting to external servers. If either of these aren't true and you choose an open source XMPP client that does only XMPP, you could modify the program by either hard coding in your server address or by having it ask a network service (DNS or similar) where the XMPP server is. No options = no problems.

I am a third year university student in the U.S. and in my experience, if given the opportunity to distract themselves from the topic at hand, students will do it. I know this because I do it in my classes right now. If your goal is to better the education of the students of your school, giving them all a laptop is probably not the answer. They don't need computers for every second of every day. Additionally, it is incredibly likely that they have a computer at home. Thus, general purpose computer labs should serve your needs quite well. That said, I think you should take a hard look at an Edubuntu (edubuntu.org) thin client setup for your general purpose lab(s). My old high school recently switched from labs full of iMacs to a labs with Edubuntu thin clients and seem to be very satisfied with the results. The first problem I mentioned, students diverting from the intended use of technology, is solved by having an "instructor" interface that has live remote desktop of all the desktops in the classroom, including the ability to remote control any given desktop. On the instructing side of things, the same software that provides the former "enforcement" functionality also allows the instructor to switch all of the clients to "demo" mode wherein all of the student desktops mirror the instructor's desktop for instructional purposes or for the instructor to allow the entire class to view one of the client desktops on a projector or large screen for presentation purposes. For more detailed information on all of those features, check out http://italc.sourceforge.net/home.php.

Obviously for content creation tasks, thin clients are less than desirable. My school has a lab of dedicated Macs for this purpose. This seems a good compromise since Macs are the industry standard for content creation.

For additional information about the setup used in the specific example I described, visit winonacotter.org, and under the offices heading, select technology. The specific hardware used can be found under the "Computer Labs" sidebar heading.

I'm sorry, this says nothing about Ubuntu and everything about your intelligence. If you really were savvy at all, you would have thought to `sudo apt-get install flashplayer-nonfree`. Seriously. It really doesn't get any easier than that. It doesn't ask you any questions. It doesn't even require that you know what website it comes from. You sir, are an idiot. Your language only furthers this opinion I have of you. Thank you for giving me a laugh and for giving me the opportunity to reinforce the suggestions of all the posts before you. You are the kind of person over which Microsoft salivates. Merry Christmas.

If you want another full-time job, get OpenMoko.