I had to look hard for this one, so please forgive me if it has been covered elsewhere.
If you get a PATH error message in a KDE app, like Kmail, even after installing Aspell, be sure to also install the aspell dictionaries! I was really flustered with this for a week until i realized I had installed Aspell without the dictionary (data) for my language.
Now misspelled words are in red, even within this text box in Konquerer.
If I may suggest something to the developers, if you continue to release a DVD version of Mint KDE it may be wise to include Aspell along with common language dictionaries.