I've seen a lot of BW mods using sprites made of SC2 models; motherships, stalkers, sentries, immortals and all that stuff. Any good tutorial on how to do this (software, etc.)? I'd love to bring some SC2 protoss tech into my BW mod.

The general guideline I can provide you is to extract SC2's models, view them in software such as Blender, and therein render isometrically into 256 colour frames. I don't know much more.

I'm pretty sure this is the general idea of what people did, although the 256 color palette specifically being the unit palette.

Cool.
Awesome question.
For starters, yes, what they’ve said is a very general outline of what you should do, though, I am unaware of blender’s ability of opening Starcraft II models.
Blizzard’s art tools are native to 3ds MAX 2011, which is what you should consider using but if you, for some reason, want to use blender and it has the ability to open M3 files then good.

Now here’s a step by step on what you should do:
1. First of all you need to extract your desired model and its textures. There’s many ways to do this, the easiest is extracting them from the editor. Find the files go to the model viewer and save the model as an .m3 file
2. Open in 3ds MAX with the Startools installed (Blizzard’s 3ds max plug ins). And setup your scene. You should have the unit with its textures applied, a camera to render the unit. How you do this is up to you. Here’s the tricky part. For large units and buildings you should render isometricaly and orthogonaly. For small units you may render at 45° either with perspective on or orthogonally.
3. Your rendered frames should now become SC-Friendly, to do this you should convert them to 256-color BMP by applying the units.pal pallete. You can do this with your favourite image editor.
4. Compile your GRP with PyGRP, RetroGRP, GRPConvert or whatever tool you prefer. And you’re done.
5. Additionally, depending on the frames, you may have to also create a iscript for said unit to work properly.
6. Put everything in your MPQ/Mod.


That's pretty much what you should do. Any additional information you require would either be a complete modeling tutorial or a modding tutorial which I just assumed you already knew how to do.

Quality post Corbo, thank you.