I am planning to use google checkout for processing orders.
On the main download page for this module, it says that it supports flat rates, item rates and table rates. But I have set up shipping based on zone rates. So will this be a problem in integrating google checkout on my website?

The only other option is paypal express checkout.

Also on the site, the customer can view the costs in a number of different currencies. Does this mean that during checkout, the customer will pay in that currency or is it only for display purposes only?

If they are able to pay using the display currency such as US dollars then once i receive the payment to my UK paypal account, will there be a small fee by paypal to convert the US dollars to Pounds?