No, but you won't be able to do an "in-place" upgrade from Vista 32-bit to Win 7 64-bit. Make sure you back up all of the data you wish to save and make sure you have the install disks to re-install the programs you want to use with the new OS.
1. http://windows.microsoft.com/en-us/windows/32-bit-and-64-bit-windows#1TC=windows-7 Can I upgrade from a 32-bit version of Windows to a 64-bit version of Windows 7 or from a 64-bit version of Windows 7 to a 32-bit version of Windows?
If you want to move from a 32-bit version of Windows to a 64-bit version of Windows 7 or vice versa, you'll need to back up your files and choose the Custom option during Windows 7 installation. Then, you'll need to restore your files and reinstall your programs. For more information about performing a custom installation, see Installing and reinstalling Windows 7.
excerpt.................. Installing a 64-bit version of Windows 7 on a computer running a 32-bit version of Windows
Before you begin, make sure that your computer can run a 64-bit version of Windows. For more information, see 32-bit and 64-bit Windows: frequently asked questions.
The Custom option installs a new copy of Windows 7 on the partition you choose. This erases your files, programs, and settings.
Back up any files and settings you want to keep so that you can restore them after the installation is complete. You'll need to reinstall your programs, so make sure you have the installation discs and product keys for the programs you want to use in Windows 7, or setup files for any programs you downloaded from the Internet. Notes
Some programs such as Windows Mail and Outlook Express are no longer included in Windows 7. If you used Windows Mail or Outlook Express as your e‑mail program, you'll need to install a new e‑mail program after you finish installing Windows 7 to read your messages or to send and receive e‑mail. For more information about programs you can use, go to Looking for Windows Mail? on the Windows website.
If you don't format your hard disk during installation, data files are saved to a Windows.old folder on the partition you installed Windows 7 on. However, you should still back up your files. If you have data files that are encrypted, you might not be able to access them after installing Windows 7. If you've backed up your data files and then restored them after installing Windows 7, you can delete the Windows.old folder.