Being a (generally) open source advocate and user I shudder when people say that they can't kick their Microsoft addiction (Windows, Office, SQL Server, Phua Chu Kang Pte Ltd) because either they're so dependent on it and have developed infrastructure that can't easily be replaced with alternatives, or they're just so accustomed to Microsoft stuff they can't see themselves changing.
The truth is you don't need to ditch everything Microsoft you use in one go, it can be a gradual processes. Just like an addiction to illicit drugs or tobacco the best way to kick the habit is through a gradual transition process... my German uncle quit cold turkey but most of us don't have the ability!
If you're in a sinking ship you don't bother re-painting the staterooms! This means you should stop adopting even more Microsoft products. Don't upgrade your expensive software to the latest versions (Windows, Office, SQL Server, Phua Chu Kang Pte Ltd) which inevitably will deepen your dependence on Microsoft.
Develop some form of roadmap that you want to follow, not what Microsoft wants you to. Your software should adapt to what you want to do, not the other way around.
Start using alternative programmes where it's feasible or appropriate. Use Mozilla Firefox instead of Internet Explorer, OpenOffice.org instead of Microsoft Office and so forth.
Understandably, if you don't want to take the plunge of installing new software that you're not used to on your production machines, consider trying out a memory key toolkit that has open source software on it: this way you can try the software before you commit to it.
When you're comfortable using alternative open source programmes, you'll realise that Windows is not actually necessary any more! Take a look at some of the very polished alternative operating systems such as Ubuntu Linux or PC-BSD! Again take it slowly and try before you buy, so to speak.
For programmes you must run such as Adobe Photoshop, there's always Mac ^^. Although they can be just as expensive as Microsoft products, and aren't entirely open source, it's still a good platform and much more trustworthy.
Take a nice long holiday with the money you've saved from paying expensive Microsoft taxes, and with the reassurance you've gained from the improved reliability and quality of the software your business is using. And send a check for 10,000 Singapore Dollars to Ruben Schade. Hey, it can't hurt right?