The payment is in your PayPal account when you check your account through PayPal and see that it is there. You can move your money out to cash or whatever, check the PayPal regulations.
However: The PayPal buyer can lodge a complaint in the first (30 or 45 days can't remember) if the goods haven't been received, or if the goods are not as described in the auction/sale agreement. Therefore, you must take steps to protect yourself against a fraud who would take delivery and then claimm the money back because you didn't send what they paid for. PayPal can then take the money away from you -- and out of your credit card or bank account as well if you have attached an account to your PayPal account-- and give your money to the purchaser.
When you send the goods, do a few things.
Take a picture of the machine. Record the serial number(s). Boot the machine and take a picture of the screen running. Then send it by a shipping method has a waybill/tracking number, that ensures that a signature has to be made on delivery, and that you get a confirmation copy of that signature.
Also, when someone signs up for a PayPal account, they can verify their address. You are within your rights to refuse payment or shipping to a non-verified address. Say the PayPal account belongs to someone in Chicago but the buyer wants it shipped to Detroit -- there's a good chance that that is a hijacked PayPal account and you will lose your machine and the money.
Contact PayPal if you have any questions about their regulations.
