1. Tools-->Half-Life-->Decompile Normal HL MDL File-->Select Model
It will "unzip" the model into several files, like reference-smds, sequence-smds, bmps and a qc file.
2. File-->Import-->Half Life SMD-->Select the Reference.smd (its mostly named after the model, for example: The reference file from the goku model may be "goku.smd")