[development] base_path() not returning path to Drupal root

[Tomas J. Fulopp]

I have one other question I am pondering for a crazy long time - I 
wonder if it's a bug in the core...?

An user has Drupal installed in www.example.com/foldera/folderb/ and in 
there a files folder ( thus www.example.com/foldera/folderb/files/ )

In my module, I need to determine the path to the 'files' folder 
relative to the domain name (example.com)

So I've used file_directory_path() .. that gave me just 'files'.
Then I've used base_path() hoping that it would give me 
/foldera/folderb/ this way
base_path() . file_directory_path()
but the result was
/files

I see this issue was discussed at length at 
http://lists.drupal.org/archives/support/2006-03/msg00042.html but there 
are no clear conclusions, and anyway, that's a thread from March 2006. 
So I wonder whether there is a clean solution for this.

I'm on Drupal 5.2, btw.

Tomas