This mod is no longer being maintained and most likely completely non-functional

Instead, try using Kyle's HealthBars++ mod, which includes more features

Mod source

Does a single thing - but does it well. Adds custom healthbars to every AIActor and Playercontroller (should be every enemy and player, basically).

1.1 - I mistyped the name of the .dll in the mod file, which caused problems on some filesystems. Windows users shouldn't be affected, but some people might've hit weird problems. Fixed now.