A networkwide client OS upgrade can be fraught with unexpected expenses, lost productivity, and bad blood between the CIO and the CFO—particularly if the company’s in-house accounting application locks up the first time it’s run under Windows XP, for example.

To help you avert the unexpected expenses, I’ve developed a simple Excel scratch sheet that can help you pull together a quick expense estimate for a client OS upgrade.

While the math is simple, the real trick in successfully estimating a client OS upgrade is to keep an eye on potential surprises that can range from licensing seat costs and custom application updates to staff training.

Tackling client OS licenses
How much will each seat of your new client OS cost? Well, if you’re using Linux, somewhere between nothing and a few bucks, depending on the distribution. Otherwise, the figure is likely between you and your vendor, and that vendor is most likely based in Redmond, WA.

Microsoft has an entire Web site devoted to its licensing programs, including an extensive glossary that goes so far as to define terms such as server for the nontechnical types (i.e., CFOs) who are interested in the topic.

Microsoft offers licensing plans ranging from five seats to 250 seats and up, depending on the size of your organization, and the option to subscribe to nonperpetual licenses. About the only thing you won’t find on this site is a bunch of dollar signs—the actual price you pay will most likely depend on your negotiations with Microsoft or one of its reseller affiliates.

In your haggling with Microsoft or another OS vendor, be sure to have an accurate picture of your client OS needs for the next two to three years, particularly when it comes to the need to run legacy versions of the OS in weird cul-de-sacs of your network. Some licensing arrangements allow you to run separate versions of the client OS on your network, whereas others dictate that you run at least sequential versions of the OS. So, if you have a room full of 486s out there in a call center still laboring away with Win95, keep issues like this in mind before signing your new Win98-to-Win2K migration license.

The right approach to Windows server client access licenses
Remember that a new client OS may be considered an entirely new client by your Windows servers, so unless you’re in a small shop or running a giant peer-to-peer network, budget a few dollars for upgrades to your server access licenses.

In the Excel scratch pad, I’ve also included rows for access license costs relating to MS SQL Server, Exchange Server, Terminal Services, Oracle, and any other third-party centralized software programs that may expect your new OS clients to pay for the privilege of speaking to them. (I also threw in a line item for growth in your number of Exchange licenses, since that’s not uncommon with client OS upgrades.) This is a fairly notorious means for software vendors to go back for seconds at the upgrade buffet, so do your homework and be prepared.

Microsoft Office, other desktop software upgrades
If you’re going to be booting users off their PCs for an OS upgrade anyway, you might want to consider going ahead and putting a new version of your company’s standard productivity software on there as well.

Dealing with custom application updates
It’s almost a misnomer to call conflicts between custom applications and a new client OS “unforeseen”—they always happen; you just don’t know where they’re going to pop up.

Here at TechRepublic, we had to make minor adjustments to a component of our content management system due to a conflict with an XP DLL. We were lucky; our development team resolved the problem pretty quickly. Talk to your ops/dev teams to check for any foreseeable complications and budget for them.

System upgrades likely need hardware boost
Microsoft’s hardware requirements for running its software typically won’t satisfy a demanding corporate user who leaves 10 programs running at all times.

Whenever you upgrade an OS, you probably need to drop a little more memory into a few desktops and perhaps replace the last of those 300-series ThinkPads that have served faithfully up to this point. You may also need to add some space to a file server someplace, so I threw in a server hardware upgrade row in the Excel scratch sheet.

Where user training comes in
The user interface of all Windows client systems has stayed pretty much the same since the quantum leap from Win3.x to Win95—that is, to a technical person’s point of view.

For some users, the fact that the XP Start menu no longer has a Settings entry is a huge adjustment. Be sure to talk to your line-of-business managers, training department, or local vendor, and plan to spend some money on user instruction.

IT staff training
While the face of Windows stays the same, the guts change quite a bit from version to version. Your team will likely need some training—this can range from a few self-instruction books for the help desk crew to updates for your admins’ certifications. Get a solid ballpark figure on these needs and include them in your cost estimates.

With the addition of the ubiquitous Misc. category, this Excel spreadsheet covers about every cost that can be associated with a client OS upgrade. Remember, as with budgeting for any new IT rollout, the real challenge is to anticipate how the technological shift will affect the company’s core business, and reflect those changes fully in your cost estimates.