How to release mouse capture in VirtualBox? I'm on my MacbookPro and using TeamViewer for remote access to my 2k3 Server. On this server I installed VirtualBox to create a virtual machine. But now I stuck at this screen and no more can use my mouse.

How can I release the mouse capture?
You need to press "host key" which is written in right bottom corner of  VirtualBox window. 

Looking at your screenshot its Right Ctrl.   

Its not default Mac Command ⌘ because you are running VirtualBox on Windows host, which you are accessing using TeamViewer. 

See virtualBox manual: link