Certain applications, such as Microsoft Word, enable you to password protect your files. Nevertheless, the zip functionality that is built into Windows XP enables the user to password protect any file by compressing it using a password. If you have an alternate compression application, such as WinRar installed then you can also use that to password protect files on any version of Windows.
To do so, right-click on the file you wish to password protect and select 'Send to...' From the sub-menu that pops up select 'Compressed (zipped) folder'
This will create a zip file with the same name as the original file.
Right-click on this zip file and select 'Explore'. This will open the file in a new window. From the 'File' menu select 'Add a password'.
Type the password in twice and click OK
Delete the original file, and for extra safety, empty your 'Recycle Bin'.
You may see the following message if you have another compression application installed. If so, just click 'Yes', and carry on as above.