Vista has a site that gives you two different tools:
1. Upgrade Advisor (scans your computer)
2. Compatibility checker (hardware + devices)
I'd suggest you use this website on a few of your main computers and figure out if your hardware is up for the upgrade. Also, make sure that the major programs your company uses will be compatible with Windows 7. This will, no doubt, be your biggest issue. You need to make SURE that everything will still work after the upgrade. If even a single program loses functionality or doesn't run properly, your company will moan and complain about it all.
I assume that the company is using Vista at the moment, right?
You'll need to send out a mass e-mail (Or, if you're not IT, have them do this) alerting members of the upgrade you plan on doing. I've never done such a thing before, but a backup of company data and important files might be something to consider in case something goes wrong.
Definitely make sure to give every employee some time before you upgrade.
Here's the website: http://www.microsoft.com/windows/com...s/default.aspx