How can I convert a model for HL for use in HL2? Is it even necessary?

I'm pretty sure you have to convert it for use in HL2 somehow. I looked in the model folders, and each model had an .mdl file along with 5 different types of files to go along with it. I assume you can't just replace the model without replacing the .jpeg, .dx80.vtx, .dx90.vtx, .sw.vtx, and the .vtd too.

it's pretty simple
you can just use the same smd
but you have to use the new compiler
the texture is the most complicated part
but you'll find what you need in the SDK
and if you wait maybe Jed will have his TGA2VTF ready :)