Well there are two different ways you can install Windows 7. One is a clean install where its like a brand new computer - all data is gone so you need to save it and re-add it (this is what I plan to do). The second option is called Windows Easy Transfer. Here is that I have read about that:

Windows Easy Transfer guides you through the process of transferring files and settings from one Windows computer to another. Using Windows Easy Transfer, you can choose what to transfer to your new computer and how to transfer it. You can transfer most files and program settings. Specifically:

• • Files and folders. Everything within the Documents, Pictures, and Shared Documents folders. Using advanced options, you can select additional files and folders to transfer.
  • E‑mail settings, contacts, and messages.
  • Program settings. Settings that keep your programs configured as you had them on your old computer. Windows Easy Transfer does not transfer the programs themselves. Some programs might not work on this version of Windows, including security programs, antivirus programs, firewall programs (your new computer should already have a firewall running to help ensure safety during the transfer), and programs with software drivers.
  • User accounts and settings. Desktop backgrounds, network connections, screen savers, fonts, Start menu options, taskbar options, folders, specific files, network printers and drives, and accessibility options.
  • Internet settings and favorites. Internet connection settings, favorites, and cookies.
  • Music. Electronic music files, playlists, and album art.
  • Pictures and video. Pictures—which includes any visual file type (for example, .jpg, .bmp, .gif)—and personal videos.
• You can read more about the different upgrades here

If you don't want to do a clean install (wiping your entire hard drive first), from all I've read you can just choose the 'upgrade' option in the installer, (if you're going from Vista x64 to Windows7 x64) and you won't lose a thing. You get that option when running the setup from within Windows itself rather than booting from the DVD to get to the setup.

I'd still make a full image of your C: drive/partition first though, and sock it away somewhere else, just to be on the safe side, which is recommended any time you do anything like his anyway. My favorite image program is True Image.