i have made some 2d animation, and some 3d animation.
now i want to blend both of them in to one animation. how do i do this?
You need to composite them together take a look at the manual
Compositor in Blender: http://wiki.blender.org/index.php/Manual/Compositing
Sequence Editor in Blender: http://wiki.blender.org/index.php/Manual/Video_Sequence_Editing