Registered: Oct 2003
Location: Northeastern Michigan, where Carhartt is a Designer Label
Distribution: Slackware 32- & 64-bit Stable
OK, here's a try at it...
You'd need a server plus 10 desktops and some laptops (no, that's not a smart alec answer; keep going). The server might be reasonably fast (processor speed around 2 GHz or more) with a reasonable amount of memory (say 2 GB or so) and one or more 160- to 200 GB SATA disk drives configured to run as a RAID array (that makes the two disks exact copies of one another so if one goes down the other is available). You'd want a DVD burner (for backing up).
You'd want one or more 16-port routers (that's your connection to the outside world; i.e., the internet, plus the internal and external network connections for your sever and desktops) if you decide to run a wired system. If you want to run wireless, that means a wireless router (or two) capable of supporting 15-20 devices simultaneously -- you are going to grow, right? (not cheap, that). You'd want one or more network printers (that connect to your router[s] with an Ethernet or wireless connection, same as the desktops).
You'd probably want everything to be Linux (makes life simple and enjoyable). If you really, really have to have Windows, get a license for VMWare Server (VMWare installs on your server or individual Linux desktop systems and runs "foreign" operating systems in Linux) and run it on there, not on any of your desktops (unless you really, really enjoy Patch Tuesday). If they're all Linux, bye-bye Samba; if not, well, you can run Samba on any Linux server with no problem.
MySQL is a data base management system that, well, lets you have one or more data bases (you know, for customer orders and the like). The P part of LAMP is for PHP, a language that connects a browser to a data base (the sort of thing, oh, say, Amazon.com does, for example). Your customers connect to your server with their browser (doesn't matter what browser), look at your product line, place an order and pay for it, all that kind of thing. That's what the combination of Linux, Apache, MySQL and PHP are for.
Oh, yeah, Apache is the service that runs on your Linux server that lets you have web pages.
With most Linux distributions you get (or can easily get) Openoffice.org software, which is a complete office system (word processing, spread sheet, presentation, data base interface, etc., etc.). Openoffice.org is free and most folks familiar with Microsoft Office will know what they're doing with it. If you persist in using Microsoft, you can install Openoffice on them too and save yourself a few thousand dollars).
What your seemingly simple question leads you to is, for all practical purposes, a full-blown business system supporting both internal and external users -- and you will need some expertise to set up and get going unless you want to learn all this stuff yourself; it's not a trivial undertaking to actually do what you're thinking about doing. Setting up a Linux system is pretty straightforward but designing and building a usable data base, building web pages, writing PHP programs to tie things together, and getting fifteen or more users happy, well, that's kind of a biggie.
A Linux server to simply tie your existing systems together wouldn't be a bad start, though...