I have just realised that when I make an order it is overwriting my admin account with details that I type into the order? Could this be because I am logged in

Yes, it's because you're logged in as admin. Although you interact under a different "role" you are authenticated as admin so if your user id is "admin" and you place an order with an email address, that email address becomes your login email (ID).

I don't consider this a bug although for "registered" users under the ecommerce role it could get confusing if you're placing an order using a different email address and all of a sudden your login credentials change without warning.

Order::set_site_currency("GBP");

I have set this but now my prices show as $15.00 GBP. I want to be able to change the symbol to £15.00 GBP. Any symbol other than $ I could search the code for it but in PHP it won't be very effective.

I've got a question. I installed the beta.
How do i change the language to Dutch in the cart. I've been looking for but didn't found???
I think i must write a rule in mysite/_config.php but dont know what.

further a few little things (bugs)

In the accountpage when updated the payment etc from the order, the status changes in the small box orderhistory but not on the detailpage. date method amount payment status and details are blank.

In the CMS undefined when you change the status of the order in the reports section.
When order fineshed-completed it notes order incomplete, but in the account detailspage is is noted as completed. But still no further info on the detailpage.

Further a little thing. When you say print or invoice in the cms it opens in the same page and not in a blank page or in an iframe.
The cms is gone and you manually have to go to the cms back again by typing the url.

Thanks for response.

Well that worked in a trunk build before 0.6 so it's possible it's been superceded by something else.