Kaos: On its own it cannot. You need an API to pass a validated token back to the script. For example PayPal API is setup with a ton of support from the dev team as well as a wide array of options and sample code for you to use IPN == Instant Payment Notification It notifies the server of a validated transaction and you can then handle it on your end. Serve up a file, create a user account etc etc.
Paypal's Instant Payment Notification feature should accomplish what you need. Basically, if configured properly, when a payment is made to your account, paypal sends an HTTP request to your server that contains the payment details (i.e. transaction id, email, payer adress, payment amount, etc.). Your script should send a request back to the server (to prevent people from sending spoofed HTTP requests) to verify the validity of the payment, and if it checks out, proceed. Try to Google 'Paypal IPN PHP tutorial' (or something along those lines).
So the only way to do it is with something like this: Fair enough... The other question I had is if this requires a business (paid) paypal account rather than a personal one.
Take a look at http://designertuts.com/paypal-ipn-receiving-instant-payments-in-your-web-application/ for your tutorial. IPN isn't always the easiet to get to grips with, but it's wonderful to use.