I want to sign up for one of the OC sites, but I don't want to use my regular email address because of all the spam. So can I just use another Yahoo email address to sign up and when I complete everything, have them send the Paypal to my regular email address instead of the other Yahoo one? Or do the sign up email address and the Paypal account address have to match?
You can just add your other email address to your PayPal account.
When you order your gift you tell them the paypal address you want the money sent to, so it doesn't have to be the same as what you sign up with.