I have Sonar Artist.  My friend has ProTools.  We would like to collaborate on writing songs and demos.  Is it possible to import/export work files between the two software packages.

Audio with no problem .... also OMF format but i can t say if artist handles it

Ephipps, the easier (and cleaner) way is to export your tracks and inport save them to a folder. 
In Pro Tools, you can inport them (make sure the tempo is the same). 
 
I tried OMF a while ago and it works, so you can try that as well, but make sure you have the exported tracks just in case... Would hate to be in a session and can't work because you can't load the OMF...