I have just started playing around with my first GIS package, QGIS. I have successfully used Ordnance Survey Vector data to create maps but when I try importing maps from an OpenStreetMap export it always gives me a birds eye view. Any idea how I can get it to produce an Aerial view?
Just guessing: You have not set any coordinate reference system for your project.
The Openstreetmap Data is in lat/lon coordinates, so should be CRS WGS84 EPSG:4326 as layer projection, which looks somewhat twisted in most parts of the world. To have the same view as in OpenStreetMap or Google Maps, use CRS EPSG:900913 or 3857 for the project, and check "On-the-fly-projection".
OSM 3D can be created but you will need to create this using more power applications
"It is used as a show case to demonstrate the potential of 3D maps as well as how 3D Spatial Data Infrastructures (3D-SDI) can be set up using standardized and open interfaces. The map display goes beyond simply rendering cached tiles that are somehow distorted in order to create a perspective effect. It is based on a scene graph model that incorporates an elevation model and as many OSM features that we could process. This scene graph can be explored using the online viewer XNavigator. Preparing OSM data to be viewed in OSM-3D requires a lot of preprocessing steps which are done on GIScience's servers."
Please read the background to http://www.osm-3d.org/map.htm
You can download the source code from http://sourceforge.net/projects/xnavigator/