What version of Photoshop are you using? With newer versions you are able to load then call app.doAction to play the loaded action while the script is running. That is as long as the script knows what the action name and set name to use.
Creating a relative path shouldn't be a problem if the document was opened from a file or has been saved. It's possible to have a document without a file path.
first of all, thanks for responding. I am running cs6. I know that i can call an action from within a script with the action set loaded. but can i run an action from the *.atn file without having to load it into photoshop?
In case you're still interested, I just released a script named Play Actions File Action (for lack of a better name) which may answer your needs; it can play a specific action contained in an actions file (.atn), without the need to load the file in the Actions Palette. This script is making use of the jamActions module, part of the JSON Action Manager scripting library. All files are open-source, licensed under the GNU General Public License (GPL) v3.