4. Go through a normal Windows 7 installation. When you get to the part where you need a product key, type in the current Windows 8 product key (if you have one) or skip the key entirely. Install your downloaded drivers.
5. Activate your newly up -- er, downgraded Windows 7 over the phone. Here's how Microsoft puts it:
The product key associated with the original Windows  software should be used for activation. If the product key has been previously activated, which is likely if the media came from a prior legally licensed version that has been activated in the past, the software may be unable to activate over the Internet, due to the hardware configuration change when installing this media onto the Windows 8... system. When this happens, the appropriate local Activation Support phone number will be displayed, and the person performing the downgrade will need to call the Activation Support Line and explain the circumstances to a customer service representative. Once it is determined that the end user has a valid Windows 8 Pro... licence, the customer service representative will provide a single-use activation code that can be used to activate the software.
Suffice it to say that downgrading Win8 Pro to Win7 Professional is legal and free, but it's a pain in the neck -- and the system you end up with may or may not be supported by the manufacturer. According to Microsoft:
In the event the end user opts to downgrade, neither Microsoft nor the PC manufacturer is obliged to provide customer product support for systems on which downgraded software is installed.
The, ahem, good news: Once you've downgraded, you can re-install Windows 8 Pro at any time.
If you run both Win8 and Win7 in a dual-boot configuration, you need to pay for both; you can't "downgrade" Win8 Pro to Win7 Professional and use both copies. You can run Win7 machines inside Hyper-V sessions in Windows 8 Pro, but problems can arise when you try to connect peripherals to your system and have them show up in the Win7 VM -- and, again, you have to pay for the Win7, you can't use a downgraded copy.
You're pretty much stuck if you have a Win8 machine and want to run Win7 on it. You could dual-boot Windows 8 and any recent version of Windows that you care to buy, but there are known problems when you install an older version of Windows on a Win8 machine. In general, the advice is to install the older operating system first, which doesn't help if your machine already has Win8.
If worse comes to worst, you can buy a copy of Win7 for $100 or so at many major retailers and perform a clean install. Just make sure to get Win7 drivers downloaded and disable Secure Boot first.
This story, "How to 'downgrade' to Windows 7," was originally published at InfoWorld.com. Get the first word on what the important tech news really means with the InfoWorld Tech Watch blog. For the latest developments in business technology news, follow InfoWorld.com on Twitter.