First of all, is this for Source or Half-Life? You should have put it in the corresponding section.
Anyway, assuming it's for HL, what is it exactly that's a problem? Are you working with brush based entities, and they won't appear, or are they point based? Most point based entities don't actually show up when you play the map. For example, a light entity would emit light from where you placed it, but you won't actually see the lightbulb sprite.)
EDIT: Meh, way too slow...