I highly reccomend using the latest PHP SDK. It is greatly simplified has many examples for every endpoint and utilizes the latest REST v0.9 endpoints. You can find it here: http://code.google.com/p/opensocial-php-client/source/checkout
I reccomend downloading the latest version from svn as the zip download has a bug in it reguarding activities which I fixed yesterday. Let us know if you have questions.
Thanks,
Jesse