I'm having grief with the new PayPal Developer site and Sandbox. I've created a personal account in the Developer but the funds I added are not showing up. I read a forum post that you had to add funds via the Sandbox login but it won't let me add funds either.
Phil
You have to login at https://developer.paypal.com with your developer account and then go to Applications->Sandbox Accounts->Create Account, the 5th field is "PayPal balance" here you can put any amount you want to your test account.