We have build an  Win 7 x64 bit image in SCCM 2007  and deploy this image to the machines.

I was wondering if i could somehow export the wim and import it in the SCCM 2012

What is the best way for me to add this image to SCCM 2012

It depends on how you created the ConfigMgr 2007 image. If you used MDT Lite Touch to create, you can just migrate the WIM image, or copy it over and add it.

If you created the mage using CM2007, the image contains the CM2007 client, and I recommend you to create a new image.

/ Johan