region specific domain?

I live in the UK and have a website hosted here with a .com extension, I have also registered my site with Google. I would like to sell some products from my site to Europe, America and Australia.
Do I need to get an .eu extension for Europe etc?
Also do I have to register my site with Google Europe, Google America etc?

thanks

For a commercial site, a ".com" would be the best way to go.
When people see an tld (such as ".eu, .cn") that they are not familiar with, they tend not to trust it as much.
".com" is more versatile, it is global.

I'm sure I've seen this exact same question over at Webmaster-Talk where I'm a moderator. Anyway, to answer it, a .com would probably be your best bet for selling globally for the reason Alex just explained.

On the search engine note, there is no Google Europe and Google America as you call it (google.com) usually lists everything that is on it's other sites - my sites are listed on both google.co.uk and google.com in similar rankings. Google.com is for all English speaking areas, where google.co.uk is supposed to remove non-UK sites from the index. If you get listed on Google, you'll be on both searches.