There's been enough written about upgrading to Windows 7 to fill a library, so you'd think PC users would understand the pros, cons and pitfalls by now.Well, not quite. Most people get the gist of their Windows 7 upgrade choices, but some tricky nuances and possible snags continue to confound consumers.C'mon, this is Microsoft. It has to be at least a little complicated. If upgrading were a smooth and easy process, that would be ... um well, that would be Apple. The Price You PayIf you took advantage of Microsoft's pre-order upgrade program from June 26 to July 11, you paid $49.99 for Windows 7 Home Premium or $99.99 for Windows 7 Professional and you are waiting for the disks to arrive in the mail on Oct. 22, when Windows 7 officially ships.If you missed the pre-order upgrade boat, the retail price of Home Premium is $119.99, Professional is $199.99 and Ultimate is $219.99.Windows 7 Bible: Your Complete Guide to the Next Version of WindowsWhat about new PC purchases? Microsoft has an offer dubbed the "Windows 7 Upgrade Option Program." Starting last June 26 and lasting through the end of January 2010, if you buy a new Vista machine, you qualify for a free copy of Windows 7. I imagine most buyers will want to have Windows 7 on new PCs after Oct. 22, but if you prefer Vista you at least have the option to upgrade to Windows 7 for free.The upgrades will be provided after Windows 7 ships on Oct. 22 and will be offered either by DVD or download, depending on the Microsoft partner.Most PCs running Vista Home Premium, Vista Business and Vista Ultimate qualify for a free Windows 7 upgrade, but all buyers should check with the retailer or PC maker to make sure their new Vista machine qualifies.The Easy Way to UpgradeSo you've got Windows 7 in hand. Now what?In some cases, upgrading will be as simple a loading the Windows 7 DVD, typing in a code and waiting about 45 minutes. Such a plug-and-play type installation (called an "in-place upgrade") is by far the most hassle-free way to get Windows 7 on your PC. You don't even have to back up your data (though you still definitely should). You will be running Windows 7 and all your applications, programs, settings, and photos and files will be as they were before. But even with in-place upgrades there's a slight catch. They only apply to those PCs running Vista, with at least 20GB of free disk space \u2014 although that should not be a problem for most users given the amount of storage on today's hard drives.XP to Windows 7: The Hard WayThings get complicated with PCs still running Windows XP. In-place upgrades are not an option here. With XP-to-Windows 7 upgrades, you will have to do a "clean installation", which entails backing up all your data, installing Windows 7 and then restoring all your data and reinstalling your applications. This is about as fun as root canal surgery.XP-to-Windows 7 upgrades call for clean installs because of incompatible applications and drivers. Also, most of the computers running XP are aged and will lack the power to run Windows 7 to its full potential. All of this makes life difficult for XP users trying to install Windows 7. Pile on fears of the same incompatibility issues that plagued XP-to-Vista upgrades and you can see how XP users are being gently forced to buy a new computer.The 32-bit\/64-bit QuestionEven if you have a fairly new PC running Vista, you may not be getting the best version of Windows 7 when you do an in-place upgrade. Why? You've got a 32-bit system. 64-bit versions of Windows are becoming all the rage. At its simplest, this refers to how much information a processor can handle at one time. 64-bit Windows can run faster than 32-bit, allows more applications to run at once and facilitates faster switching between apps.You should understand, however, that to get the full benefit of a 64-bit OS and 64-bit compatible hardware, you'll also need 64-bit applications \u2014 and application developers are still lagging behind Microsoft and Intel on this front. Your favorite and most demanding apps may not have been rewritten to take advantage of 64-bit technology yet.Most PCs sold in the past three years have 64-bit compatible hardware and most sold in the past nine months run a 64-bit version of Vista. So if you've got one of these, and want to upgrade, just load the 64-bit Windows 7 disk (Windows 7 retail packages come with both 32- and 64-bit disks) and let your in-place upgrade to 64-bit Windows 7 begin.But if you're like me and your laptop runs a 32-bit version of Windows Vista, your only in-place upgrade will be to a 32-bit version of Windows 7. To go from 32-bit to 64-bit, you will have to do a clean install. Additionally, you'll have to add RAM if you have anything less than 4GB, because 64-bit demands this much at minimum for good performance.You could upgrade your Vista machine from 32-bit Vista to 64-bit Vista first, and then do an in-place upgrade to 64-bit Windows 7. But in addition to buying a Windows 64-bit Vista disk and buying more RAM, you'd still have to do a clean install for the 32-bit Vista to 64-bit Vista upgrade.Is it a disadvantage to run a 32-bit version of Windows 7? Heck no. Most users run a 32-bit OS very comfortably everyday. With 3GB of RAM, a 32-bit OS can easily handle aggressive computer use (unless maybe you're editing the next Spielberg movie on your laptop.)But if you're a forward-looking power user with the latest hardware who usually has 10 apps going at once, then 64-bit will be worth the dreaded clean install.Are you a Tweeter? Follow me on Twitter at twitter.com\/smoneill. Follow everything from CIO.com on Twitter at twitter.com\/CIOonline.