What do you call this sort of vent?
 

The one on the garage above the window?

http://pictures.realtracs.net/135100...1351264-20.jpg

Looks to low to be a vent, on the main house the one at the top is called a gable vent.
Pictures take way to far back to be sure.
http://www.alvcompany.com/halfround.html

If it's not vented then it's an arch.
http://www.architecturaldepot.com/AR...on-arches.html

+1

The triangular section on the main home is a gable end vent.

The half moon section above the other window is either a half round window or a decorative half round header.