(coco) Aspell and Lyx - how to add a Personal Dictionary file?

[Dr . Joachim K . Rennstich]

I am successfully working with Lyx 1.6.1 and my installation of coco- 
Aspell on my Mac with OS X 10.5.6. I have not been able to get the  
spelling checker to ever learn a word. Under "Preferences > Language  
Settings > Spellchecker" I have an option to add a Personal Dictionary  
"Other than the default" - since this default doesn't seem to work,  
how can manually add personal dictionary? What kind of file do I need  
to create that will show in the dialog box as a selectable file? A  
simple .txt file (e.g., personaldict.txt) won't work.

Any suggestions would be most welcome - thanks in advance!
-Joachim