In some of the more recent builds of MOSS, the "contains" and "does not contain" options for advanced searches have been removed. This was done because of query performance concerns expressed by a significant number of customers. If you are not worried about the query perfomance hit, you can make this option available to users with a small amount of work. Take the following steps to do so.
1. From your search center, go to the Advanced Search Page
2. Click Site Actions->Edit Page
3. On the “Advanced Search Box” web part, click edit -> Modify Shared Web Part
4. Expand the Properties tab
5. In the “Properties” textbox, find <Option Name="AllowOpContains" Value="False"/> under root the node. If it does not exist, create it.
6. Change value from “False” to “True” and click OK
7. Click “Publish” to publish the page
Now the user should see the “Contains” and “Does not contain” options. The changes were only made to the Search UI. No changes have been made to the search object model, so any custom searches using "contain" operators will stuff function correctly.
(Note that this is a manual step. If you have a large number of search centers across multiples farms, it is possible to script this with the object model)