This could be the guide for you.
In one of my previous positions, I was the Internet Administrator for a law firm who, at the time, had around 500 employees. They were largely Internet newbies with an antiquated e-mail system based on Banyan Vines and an Internet pipe smaller than the one my Grandad used to smoke. Within 6 months of me taking over, they were using Linux to run their new fast Internet link and they loved it. Here's a few pointers on how you can make your company make the switch.
1. Hardware
One of the best things about Linux is that it will quite cheerfully run on hardware that NT would spit at. In any large corporate, the IT department has a store cupboard where old hardware is left to collect dust in peace. Don't try and suggest buying new hardware for your Linux gateway, getting a big company to spend money on something it doesn't have an interest in is an exercise in futility. It won't happen. You can always upgrade the hardware after you've proved the idea is sound. To give you an idea, the first demo server I built for the above company was a rather nice Pentium 200 with 64mb of RAM and a 2gb hard drive. Barring the problems caused by potential hardware failure on a system like this, this proved to be a more than adequate platform to handle the Internet needs of 500ish users.
2. The Linux Distribution
Nearly the first thing you will be asked after you suggest this to a corporate IT Manager is 'So, when you get run over by a bus, who's going to support it?'. This is a very pertinent question and one I've yet to find a universal answer to. One word seems to have a lot of effect in this case and that word is 'Redhat'. Redhat have now managed to get themselves into a position that's synonymous with the likes of NAI and VA Systems. IT managers like hearing names they've heard before. Mention 'Slackware' or 'Mandrake' to them and you may as well install Wingate and be done with it. Use Redhat, it works, it's easy and you can replace it with Slackware later.
3. The PackagesYou're not going to be taken seriously unless you can prove that what you're doing is going to make the Internet lives of your co-workers a happier and faster one. Don't mumble on too much about security other than in the general sense of there will be some and it will be at least comparable with what you have - you're on NT, remember. Mumble on about bandwidth saving, mumble on about usage reports (see next paragraph), mumble on about how it will work seamlessly with your existing security system (that's NT again). To cut this short, here's a recipe of programs that will get you on your way:
Squid - You need Squid. Everyone needs Squid. This is not optional. Squid is arguably the most useful program on the planet. It's a web proxy with a mission in life and that mission is to make your users love you until it hurts. Squid will save you bandwidth, it will speed up your users perceived web response, it will block adverts, it will authenticate users with their existing NT username and password and, most importantly of all, it will make your HR department happy. Not too many clues here but: 1) Squid makes lovely logs files. 2) Perl is pretty easy to learn. :).
Webmin - Webmin is what you use to keep the Windows NT Administrators in your life happy. In short, it's a web based configuration tool for Linux and many other UNIX like operating systems. It can manage nearly all aspects of a Linux system (including Squid) so this will negate any opposition from those NT Admins who haven't quite figured out what a CLI is yet. It's a snap to install and quite cheerfully supports SSL - your manager has heard of SSL, it's a TLA he likes.
IP Chains - This is a firewalling system that is part of the 2.2.x and later kernel trees of Linux. The IP Chains HOWTO is arguably one of the finest examples of good documentation. Read it, learn it and then wipe the silly grin off your face and get a basic packet filtering firewall set up.
Sendmail - Sendmail is one of the nastier packages to work with in terms of newbie friendlyness. Many people will try and persuade you to use something else. Suck it and see. Sendmail, however, is well supported by Webmin and this is where you get brownie points. Don't make the mistake I did, don't try and replace your corporate mail system with Linux, Sendmail and POP accounts, you'll fail. There is currently, to my knowledge, no groupware package for Linux that can hope to come close to the capabilities of Microsoft Exchange. Big companies like Exchange, little companies like Exchange, I like Exchange. Try a little reverse psychology instead...
4. The Reports
The Internet for many companies is a bit of a liability. Whichever website you enter, the chances are that your IP has been logged in a file and is used in some kind of visitors report by the site. Squid will help you here, Squid can be configured to minimize the amount of information that's broadcast about you when you visit a site. Either way, the IP can be tracked back to the owner and therefore if your companies IP is found connecting to, shall we say, adult content sites, this could lead to public embarrassment for your company. You can very easily write (or even buy) programs that will show you exactly who visited what site at what time. Spying on your users isn't too pleasant but, from a corporate view, is essential to prevent lost revenue and liability. Provide these reports using Linux and you'll have one more reason why Linux is essential for your company.
5. Stability
This is the one I enjoyed most. My company at the time actually hired a UNIX specialist to fill in for me while I was on holiday. Just in case something with the Internet gateway broke and they couldn't get in touch with me to fix it. Did it break? Nah :)
To paraphrase a recent popular film, this article is merely intended to show you the door to the world of Linux, you must decide whether you, and therefore your company, will walk through it or not. Linux is there, it is commercially viable and I hope it can show you what your local MCSE doesn't want his users to see, a world without NT.