You can usually change the currency during the setup wizard for a new customer, however you may have to use the foreign trader wizard. This, i understand can only be done in the professional version.
If you have the professional version then go to "Modules" along the top, scroll down to "wizards" and hover over it a sec. In there is the foreign trader wizard.
Follow it through and then you can select the currency from the drop down during the "New Customer" setup wizard.