Hope this helps
Yes we have implemented the paypal plugin successfully into Silverstripe
First of all download the paypal.rar file from here http://open.silverstripe.com/ticket/1760
Copy PayPalPayment.php from the archive to [yoursite]/ecommerce/code
Open up this file and set self::$payPalRealAccount to the paypal email address of the merchant account
Copy PaypalPaymentPage.ss to [yoursite]/ecommerce/templates/Includes
Go to your _config.php file for your site....usually located under the mysite folder and add the following code to it
// Define which payment methods your site uses.
'ChequePayment' => 'Cheque',
'PayPalPayment' => 'Credit Card'
If you aren't going to accept offline payments then remove the chequepayment line
Finally run db/build?flush=1 and that should be it