the problem with paypal standard is that it is not a real time payment gateway.
with paypal standard you need to set up an IPN Page that will receive the results of the paypal transaction when they process it on their end.
on the IPN Page you can configure it to send the email receipt.
see the paypal documetation for IPN:
Uncheck the Create a file for this email option, and you will have the DW Edit icon to use fro setting the mail body.
a search of this forum for IPN Will give a lot of additional info as well.