When you use decompiler, it decompiles the .MDL file into .SMD files, they are created in the same
directory where your model is, if you don't change the directory. There may appear more then one
.SMD file, then one will be the model and others will be the animation sequences for it.
After decompiling press File->Import->Half-Life SMD and choose your model's file, later if
you need the animations, open your model and press File->Import->Half-Life SMD, then
select animation file that you need, you can import more than one animation into your model.