You can do it also by hooking NtMapViewOfSection and getting name of mapped section, if it matches wanted dll, look in pe header of mapped dll for entrypoint and hook it
That's the simplest way.
Somebody in the past also asked how to know when dlls are loaded, and I will also point to same code : http://deroko.phearless.org/itracer.zip <--- look for hook of NtMapViewOfSection. There is detailed code how to find dll name too
As you may see from previous answers, there are many ways to do it