Picassa 2. I run Windows XP and I use Picassa 2 to import and handle my photos. Whilst it is easy to use, it will not allow you to import to an existing folder.
The pop-up display which comes up early in the importing procedure asks for a folder title. It will not allow you to select an existing Picassa folder, and even if you type in exactly the same folder title you have already used, it just starts another one.
This problem is not unknown and Google (Whose application this is) answers this question, but their advice does not work.