Later in the review we'll be looking more closely at the different versions of Windows 7 and how they vary, but realistically you're looking at either Home Premium or Professional since the much talked about 'Starter' version is OEM only, Home Basic is a) crippled and b) for 'Emerging Markets' only and Ultimate is only really worth it for those desperate for the extra functionality.
In any instance we'd recommend opting for a full, clean install where possible. If you've stuck with Windows XP then this is unavoidable - you can't upgrade from XP to Windows 7 - but if you've got Vista then you can upgrade to Windows 7. This includes OEM installs, so if you're using a laptop or PC that came with Windows Vista, you can upgrade to a corresponding version of Windows 7. For more details on Windows 7 upgrade paths take a look at the TechNet entry for it.
Microsoft provides a number of applications and services to help make the switch easier. This includes the Windows 7 Upgrade Advisor (a downloadable application that will advise you on hardware capability/compatibility and upgrade eligibility), the Compatibility Center (a website for checking software and hardware compatibility) and Windows Easy Transfer. Easy Transfer, which helps migrate user accounts, settings and data, can be used with an external hard drive, dedicated PC-to-PC cable or via a home network. These are all useful tools, although more experienced users may find it unnecessary to use them, especially since even a clean install dumps your previous Windows program and user folders in a separate folder.
As Ed discovered when he was working on the Windows 7: Performance Analysis article, it's easy to forget how irritating Windows XP installation sometimes was and in comparison Windows 7 is a breeze. This is particularly true when doing a clean install, which is no more difficult than installing some dodgy, malware toolbar. In our experience it will take anywhere between 15 to 30 minutes depending on the speed of your machine. This is why we'd always recommend doing a clean install: it takes less time, is easier and is less prone to errors and problems further down the line. For reference a clean install of Windows 7 Ultimate, the version we're using for review, takes up around 10GB of hard drive space.
In comparison taking the upgrade path is the proverbial "how long is a piece of string?" affair. One of our test systems, which has been in use for several years and has been upgraded from Windows XP to Vista and then to Windows 7, took over 12 hours - we can't tell you exactly how long since we missed the end of it!
On the whole, though, the Windows 7 installation process is pretty painless and largely idiot proof, too. It also helps that, provided you're not using particularly obscure hardware, drivers for most common components are included. As such you'll be presented with a PC that's ready to use, rather than one that's ready for a few hours of tedious driver searching and installation; connecting to a wireless network is even part of the installation now. This is a pretty fundamental improvement over Vista, made all the better by driver updates now being accessible via Windows Update as well.
Unfortunately, due to our review code being an RTM (Release to Manufacturing) version we weren't able to sample the new web browser ballot screen that'll come with retail boxes in the EU.