First, make sure you're putting the action in the right place.
ATN and PNG files go here:
Macintosh HD>Library>Application Support>Adobe>Photoshop Elements>6.0>Photo Creations>photo effects
(NOT in Your username>Library>Application Support... etc.)
XML Files go here:
Macintosh HD>Library>Application Support>Adobe>Photoshop Elements>6.0>Locale>en_Us>Photo Creations Metadata>Photo Effects
For the XML File:
Open any xml file in the folder by choosing open with>text edit. Before you change anything, do file, save as: Your Action Name.xml in that same folder.
Then, find this line:
name id="Name" value="Whatever Action You Opened" localize="true"/
and change the bolded part to the name you want to call the action you're installng.
Then, if you want to put your installed actions in their own category, you'd find this line:
typecategory id="TypeCat" value="Category of action you opened" localize="true"
and change the bolded part to the category you want. For example, I have all the actions I've installed from CoffeeShop actions in a folder called Coffee Shop Effects.
Save that xml.
Now, go back to:
Macintosh HD>Library>Application Support>Adobe>Photoshop Elements>6.0>Locale>en_Us
Rename MediaDatabase.db3 to MediaDatabase.old
Open PSE. It will take awhile to load because it is re-doing the media database. When it opens, you should open your actions panel. If you put the action in its own folder (in teh XML file editing step), you should see that folder name in the drop down menu. If not, you should see it in the all actions category.
When everything's working right, go back and delete mediadatabase.old in the Macintosh HD>Library>Application Support>Adobe>Photoshop Elements>6.0>Locale>en_Us folder.
Also, be sure to check out my tutorial on installing layer styles, which can be found at this link!!