There are two options to checkout as a guest.
First make sure you are logged out by clicking the "Logout" link near the bottom right corner of the page.
Click the button near the bottom of the shopping cart page.
Simply enter a fictitious email in the email field. For example: firstname.lastname@example.org
Do NOT create a username and password.
You will have an opportunity to view your order confirmation on the success page. If you wish to have your tracking number emailed to you - email email@example.com referencing your order number.
Select the button towards the bottom of the checkout page.
Even if you don't have a PayPal account you will still be able to checkout.
After clicking the PayPal button look for the "Check Out as a Guest" option on the following page. On the page that follows, click "Don't have a PayPal account?" and then fill in the form that follows to place your order.