You can block all overseas bidders from bidding if you want to!
Go into your 'My Ebay' page
Box on left at the bottom entitled 'related links' click the bottom option entitled 'more'
Managing your items - click on 'block/pre-approve bidders'
In the 'Buyer requirement prefs' select 'are registered in countries you don't post to'
There are other useful options in there as well.

Alternativly to the above just click the link below lol
http://offer.ebay.co.uk/ws/eBayISAPI...ockPreferences