Version:            (using KDE 3.5.9)

Consider modes:
X contains Y
X has an attachment ...?

This does not make too much sense and the UI is quite different from find dialog. I would suggest for each entry of the query add the content of find dialog with addition of attachment:


X ([ ] does not) match(es) criteria:
contains text ..........
[ ] whole words [ ] case sensitive [ ] regexp 
[ ] attachment

of course this is only ASCII draft :-)

In total:
* improved readability
* one negation
* two more options
* consistent UI
* more weekend-user friendly while not limiting power-users