It's fairly simple, but a direct port would look like arse (and it isn't the world's most beautiful model to begin with). I believe a character model is one of the few steps forward MSS made, but I'd have to dig through the massive archive to find it, and dunno if I could view it with what I've reinstalled so far.
Does it count as a Necro if it's the post at the top of the forum..?
I can't figure out how to port goldsrc model to source, did you have the process written down somewhere? I just can't find the ressources online.
Been so long since I've done it... If ya open the SMD's with notepad (or such), you'll find they are fairly similar, and you can fix the differences with some S&R. After that, it's just a matter of ripping out the physics mesh, converting/resizing the textures, and rigging up an older style QC (which, IIRC, sometimes just involves removing some lines from the Source QC.)
edit: @Truewarrior I'm on crack and doing this the wrong way around, aren't I?
Okay, the other way is actually simpler, but ultimately futile. Import HL1 Mesh, export Source Mesh. If you're using Milkshape, similar, use the HL1 mesh, export with bone weight, tweak the SMD with a text editor to match the formatting of a Source SMD you have laying about via search and replace until the syntax matches. Then you can duplicate that SMD to use as the physics mesh - just replace its texture with the standard physics one from one of the models in the SDK.
It'll work but... The result will look absolutely awful in Source. To make it look "reasonable" you'd have to either subdivide or use the D3D polycount tool, (the latter of which means re-rigging the bones all over again but makes a much more sophisticated conversion), the maybe give it a 0.01 bloat filter ("big boy" in Milkshape3D plugins), then TRY to increase the texture size to say 2048 or 4096, make it a VMT with the VMT converter, define materials etc (UV/bump map, etc - all sorts of tutorials for that out there). THEN you might have something that may look somewhat reasonable in source, if a little balloon like, but at that point, you might have well have done it from scratch, for all the effort you've saved.