For most would-be Windows 7 users, a 64-bit version of Windows 7 is the right move. But if you don't have sufficient RAM (at least 4GB), or you rely on devices that don't have supporting 64-bit drivers, or you need to upgrade an existing 32-bit installation, 32-bit Windows 7 might be the better choice. A few editions of 64-bit Windows 7 provide a Windows XP Mode that solves some backward-compatibility problems, but it isn't a universal panacea. In speedy Q&A format, here's just what you need to know.
Q. Is my PC supported under 64-bit Windows 7?
A. Most PCs manufactured in the past three years (i.e. after Vista's debut) are capable of running 64-bit Windows 7. The exceptions are those that ship with low-end CPUs that don't support the AMD or Intel 64-bit extensions. Examples include Intel's Atom line of low-powered CPUs and early Intel Core CPUs, like the Core Duo (not Core 2 Duo). If you're not sure what kind of CPU is in your system, or whether the CPU supports 64-bit operation, you can use the free Intel Processor Identification Utility to find out.
Q. What about all of my peripherals?
A. As with PC support, most peripherals manufactured in the Vista era work with 64-bit Windows 7. However, legacy hardware support is a hit-or-miss proposition. Some manufacturers -- for example, vendors of network interface cards or disk storage controllers -- are more up to date than others, thanks in part to the fact that they've been supporting 64-bit computing under Windows Server since the 2002-2003 timeframe. Devices that don't have obvious ties to the datacenter (such as custom input devices, multimedia hardware, and some printers) can be harder to integrate since they were manufactured at a time when 64-bit desktops were a rarity. Your best bet is to do a Web search to see if the manufacturer has published a 64-bit device driver and, barring that, if other users have come up with a solution.