I don't see why a search for *.jpg would show any *.xxx file. Something must be wrong, either in the way you do it, or in your computer.
Still, all you've got to do is indicated by the first line of your post: create multiple users. If you make an account for your children (either one account for each one, or one for all of them together) or let them use the special Guest account, they will be unable to see any of your files. Not only your jpg-files will be unreachable, but also all of your mail and documents and IE-history.
Three things to note:
1. Don't give them administrative capabilities or they would be able to see everything.
2. Anybody knowing the password of the system administrator account (which is empty by default) can grab the ownership of all files, if knows how to do it.
3. As an extra security measure you can make your My Documents folder 'personal' as described in http://support.microsoft.com/kb/304040 Then not even administrators aren't allowed access.
The big question to me: why did you opt for single user if so obviously it doesn't work for you in your situation.
Using xp home, sp2, all updates. Single user.
I save business Screen Shots as JPG files.
Occasonially I let my grown children use my computer.
I would like to hide the business JPG files so they could not be found by Win/Search.
I tried changing the JPG extension of the file to "000" and "XXX"
SOME ( not all) of the files still show up with " *.JPG Search", showing the 000 or XXX extension and PSP WILL OPEN them like they were JPG files.
What can I do to prevent these from showing up with a *.JPG Search?