Hi Kaj,
There are two ways you could accomplish your tasks:
First, you could actually send the newsletter Email Send to yourself. As Nisha mentioned, there is a known issue that we are working to resolve with the Test emails in the EU. When the email arrives in your inbox, there will be a pre-header that says "Click here if you are having trouble viewing this message." When you click this link, it will take you to an in-broswer rendering of your newsletter. You can share this link with your colleagues, but please note that the tracking script will associate any click events with your record in CRM. Alternatively, you could use the Freestyle or Custom HTML editors to access the code for your newsletter email template. You could then create a landing page, place this code there, and share this page with your colleagues.