Yep, thats simple. Here's how to do it:
Go to any folder, then Tools->Folder Options and select the File Types tab. There are two entries -
Code:
(NONE) File Folder
(NONE) Folder
Select either of the two and click Advanced. Here, the "Search" option should be in bold. If not select the other one and try. When you find that, just click the "open" option in the list and click Set Default. Click OK twice and the problem should be solved.