its a bit complicated i think.
I only have experience of paying into a german paypal account, but basically i had 2 choices:
1. pay them in GBP, paypal converts it and charges a fee (20 quid odd i think)
2. change your primary currency on your own paypal account to euro, then pay with that (paypal charge no fee but give you a gash exchange rate)
Basically the lesser of two evils for me was to change to euros, pay and accept the crap exchange rate (lost 12 quid IIRC) and change back. the loss of euros on the exchange rate was lower than their fee.
Not sure how this translates the other way but the paypal site does explain it somewhere.
hth
Dave