After having spent several months extensively testing Windows 7, I have found that there are significant bugs in the upgrade process. Some of these are Microsoft's fault, some of these are simply that the upgrade does not always set the proper drivers for hardware and peripherals.
First, you will generally have good success doing a clean install of Windows 7. This allows Windows 7 to find and install any known drivers as well as to avoid conflicts with currently existing software and peripherals. The Windows 7 compatibility test is not either borrow or sufficient in many cases when performing an upgrade. For example, Windows media player in Windows 7 does not always set the correct video or audio codecs. In such cases programs like Camtasia Studio 6 may not work properly. The same applies to other applications.
Second, Windows 7 upgrade may accept some of your current drivers. However, the Windows Vista drivers are not necessarily Windows 7 compatible or compliant. This holds true for USB drivers (USB host controller), soundcard drivers, video drivers, and some hardware peripheral drivers. This is why a clean install works better overall.
Third, one of the problems that has already been reported on this forum is likely at the root of upgrading Windows Vista (32 bit or 64-bit) to Windows 7. That is, the DNS search functions dialogs closing spontaneously seems to be linked to upgrading from Windows Vista to Windows 7.
Fourth, not all Windows Vista drivers (32-bit or 64-bit, but primarily 64-bit) are not necessarily compatible with Windows 7. Once you have performed an upgrade you should go to the manufacturers support site, download, and install their current Windows 7 drivers. In some cases, such as Creative Labs audio drivers may state the obvious. That is, that their Windows 7 drivers appear to be the same as the drivers already installed (Windows Vista). However, they are not. The current drivers are more recent and designed specifically to deal with complex issues regarding sound cards and 32-bit/64-bit drivers. So, what looks like it is the same, is not the same. The same applies to ATI and NVIDIA drivers, whether for motherboards or graphics cards. If you are upgrading from Windows Vista to Windows 7, you should always download and install the latest drivers posted on the manufacturers website. They are correct even if they look the same as the ones you currently have installed. Do it anyway. Some manufacturers still have problems with their Windows 7 drivers. ASUS for example is a slow on the uptake for both their motherboard and soundcard drivers. Some of their drivers are still not Windows 7 compatible, although most of them have problems with the 64-bit versions not the 32-bit versions. Make sure that you have the current motherboard BIOS and chipset drivers. Particularly the Chipset updates may be necessary for proper soundcard operation, and specifically relative to USB.
Fifth, you should uninstall printer drivers, any USB devices or Bluetooth device drivers before performing an upgrade.
Sixth, always, ALWAYS, uninstall DNS before upgrading any version of Windows (XP or Vista). If you don't, you're very likely going to have problems and you can only kick yourself for that. Microsoft could give a hoot about any potential problems with DNS and doesn't report it as a potential problem. Believe me, it is, or at least can be in many cases. So, uninstall DNS first. Also, uninstall any applications that the Microsoft compatibility test highlights. Some of these applications can cause conflicts with other applications, as well as with Windows 7 itself.
Lastly, there are a couple of ways that you can get Windows 7 installed cleanly:
1. Boot from the CD and allow a clean install. This will save your old Windows to Windows.old. From there you can recover all your documents and settings and any other information that you need without impacting on Windows 7. If necessary, you can always uninstall Windows 7 using this procedure. Always do a backup of your current Windows install before upgrading just in case.
2. Do a completely clean install by first making a backup of your current Windows, reformatting your hard drive, and installing Windows 7. This is a tedious procedure because you have to reinstall all your applications. However, by doing this you will absolutely minimize any problems you might have with the Windows 7 install, and in most cases eliminate all of them. Once you get Windows 7 completely installed and before you install any of your applications, make sure you have the current Windows 7 drivers for all your peripherals (sound, video, chipset, etc.). Make sure that they are all current and fully support your version of Windows 7.
3. I'm not sure exactly what versions of Windows 7 relative to Windows Vista the version of Windows 7 that you are installing will allow. I haven't been in a position to test that. For example, I'm not exactly sure whether Windows 7 Home Premium will allow the install of that version to upgrade Windows Vista Ultimate. I suspect it will not. However, if it does, stop right there. Never, NEVER, attempt to upgrade any higher version of Windows Vista to a lower version of Windows 7 even if it allows you to do so, which it probably, as I've said, won't. Nevertheless, don't even try it. Basically, FAGETABOUTIT!!!. Do a clean install.
4. You can upgrade your system's BIOS before you upgrade to Windows 7, but you should wait until after Windows 7 is installed before installing any new Chipset drivers. Remember, the chipset drivers are key to handling certain peripherals like USB host controllers and related issues.
Your best bet for the fewest problems, particularly with DNS, your video cards, and your sound cards, is to do a completely clean install and reinstall all your applications afterwards based on the above recommendations. It will take you less time to do it this way than it will to clean up the mess that can be created by performing an upgrade. There are enough differences between the way that Windows Vista handle certain things and Windows 7 handle certain things that the potential for problems is more likely than not. I have run into most of these. However, I have not run into any of that after doing a clean install with regard to both Windows 7 32-bit and 64-bit. However, I will say this, Windows 7 64-bit upgrades are the most problematic. So, if you're planning on going form Windows Vista 64-bit to Windows 7 64-bit, be prepared. Although it doesn't occur in every case, you will most likely end up being SOL.