How can I use the newly revamped Dropbox-PHP API?

I would like to use the Dropbox-PHP API that has recently come under development again. It is located here: http://code.google.com/p/dropbox-php/

I did cloned it with hg clone https://dropbox-php.googlecode.com/hg/ dropbox-php and I get this file structure:

Dropbox/API.php
Dropbox/autoload.php

Dropbox/Exception/Forbidden.php
Dropbox/Exception/NotFound.php
Dropbox/Exception/OverQuota.php
Dropbox/Exception/RequestToken.php
Dropbox/Exception.php

Dropbox/OAuth/PEAR.php
Dropbox/OAuth/PHP.php
Dropbox/OAuth/Zend.php
Dropbox/OAuth.php

examples/accountinfo.php
examples/createaccount.php
examples/download_image.php
examples/getmetadata.php
examples/oauth_workflow.php
examples/uploading.php

But I get this error when trying to run accountinfo.php (or example):

Warning: include(Dropbox/autoload.php) [function.include]: failed to open stream
No such file or directory in dropbox-api/examples/accountinfo.php on line 7

Right, so then I move the Dropbox folder inside of where all the example files are and still get an error message:

Fatal error: Uncaught exception 'Dropbox_Exception' with message 'The OAuth class
could not be found! Did you install and enable the oauth extension?' in
examples/Dropbox/OAuth/PHP.php:36 Stack trace: #0 examples/accountinfo.php(9):
Dropbox_OAuth_PHP->__construct('', '') #1 {main} thrown in
examples/Dropbox/OAuth/PHP.php on line 36

So I'm obviously not doing something right but I have no idea what.

Also saw on the site where it has instructions on installing:

pear channel-discover pear.dropbox-php.com
pear install dropbox-ph开发者_如何转开发p/Dropbox-alpha

I ran those two commands and it still won't work. I don't usually have any problems coding in PHP but the lack of documentation is a little frustrating.

Update

As noted in the accepted answer below my main problem was not having oAuth installed on the system. I'm running OS X 10.6 - if someone can provide some clear and easy instructions on how to build / install this to work with XAMPP / PHP 5.3 I will accept your answer. I've tried the articles online about using homebrew and such but these are flaky and do not seem to work for me. Guessing I will have to build / install it from scratch.

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The Dropbox folder needs to be inside one of the folders in your include_path.

Edit:
Also oauth needs to be "installed" on the system and included in php.ini (when you do phpinfo() oAuth should show up as a module). then things should work.