No, but if you have Windows Vista Service Pack 1 (SP1) installed, you can pause the index for 15 minutes at a time. For more information about installing Windows Vista Service Pack 1 (SP1), see Learn how to install Windows Vista Service Pack 1 (SP1).
The Windows search index improves the efficiency of your searches by keeping track of file names and important file properties for most of the files stored on your computer. The index is what makes it possible for searches to take just a few seconds instead of several minutes. The index is always on, unless you pause it, because it is essential for fast searches.
When the index is running, it generally won't affect your computer's performance. When you make changes to files, however, the index quickly updates those changes, momentarily putting a small additional load on your computer's resources.