The control panel in 1&1 looks a little bit different than other domain registrars, but the DNS changes can be done easily by following a few simple steps. (You can see a video version of the tutorial at http://www.youtube.com/watch?v=csQLCaUjHeY)
To connect your domain:
1. Log into your control panel at 1&1 to the Domain Overview.
2. From the menu above the domain list choose New> Create sub domain.
3. A new window will open. In the info field add WWW and choose the domain you are connecting from the dropdown menu. Click OK.
4. Back in the overview check the new sub-domain you've added and choose from the menu DNS> Edit DNS Settings.
5. You will reach a DNS settings page. Choose General settings: CNAME and add the alias www.im-router.com. Confirm and click OK.
6. To connect the A record choose the main domain name in the overview, choose again DNS> Edit DNS Settings.
7. This time choose DNS Settings: DNS.
8. Under Advanced DNS Settings choose IP Address: Other IP address and add the IP 188.8.131.52. Click OK.
It can take up to 24 hours for the DNS to propagate and your site will be up and running :)