Hi Martin,
As you mention your environment is fine. There is required minimum configration from server side to enable the elipse base development.
There are 2 possibility for failure of create project.
1) Check with you basis team, All neccessary configraion in place in sap server side.
2) Please check eclipse base development invironment installed correctly in you system with administrative right of you system while installing the eclipse and ADT(.i.e. Install all the eclispe and ADT with administrative right of you PC)
3) It required special authorization to you user id for access to ADT.
Please check the below link http://www.sdn.sap.com/irj/scn/go/portal/prtroot/docs/library/uuid/d018987d-0417-3110-fd83-9c5f193f2b90?QuickLink=index&overridelayout=true&59407987709596http://