Finding the users folder

I would like to create a folder and write a file to the application data folder of the current user.

How can I find the path to the current user's application data folder?

This is a typical path:

C:\Documents and Settings\UserName\Application Data\MyApp

but I guess that most of it is configurable. ie Doc & Sets may be on D:\ .

Is there a win api function that will return the file path to use?

Thanks in advance,

Mike