You will need him to export all the individual tracks as separate WAVS. I recommend doing them all from start to finish otherwise you'll have to spot them at their exact positions (so in other words, each wav is the exact same length)..
If there's MIDI in the session, he can export the MIDI files individually too.
Import all the wav's (and MIDI if there is any) and they should be in sync if he has exported them correctly.
Any plug-ins etc. that he has in the session won't be transferred over, but if he exports them with the effects already on them, you won't need them.
This isn't an ideal way to do it, and if you two will be collaborating a lot, I'd recommend one of you makes the switch to the other's DAW. That way you can just copy the whole session folder and it will run the same (bar any plug-ins that one has but the other doesn't).
Hope this helps, get back to us if you have any more problems.