Maybe send as mpeg2 files, so it won't matter much if they use mac or pc?
Did you give them all a DVD copy, btw? If so, they can probably just pull what they need.
If they need anything in particular in HD for their reel, they can then simply reference the time on the disc and you can render an HD file for just what they actually want. Saves you from randomly putting together clips they may (or may not) want.