Thanks for the info, guys. I figured out the whole thing pretty much straight after I'd made my post. I was just confused because you can't use hyphens on the PayPal website, which is why I went and typed in my card number, rather than my account number, which has two hyphens in it.
Basically, all I had to do was remove the hyphens from the number next to "ACCOUNT:" which you can find on the back of your card, put 9000 as the BC number, because the bank I use is PostFinance, and it worked. It took a few days -hence my delayed reply- but everything's in order now. Whatever money I don't spend can be put right back into my bank account.
Might as well post the details for others who may be as clueless about it as I was.