1) custom Look (aka Windows, Taharez)
You can make up a new dll. There was been discussion about a data driven way of customising the appearence. If you look at the code, its almost all setup and simple layout code, which could be specified in a data file instead. The bad news is this hasn't been done yet.
2) Create the '.font' files
Just edit them in a text editor. It just references the font file and has some extra info.
3) create imagesets & '.tga' files
Text editor and photoshop, I imagine.
4) create '.schema' files
Text editor - it just lists the widgets that can be created by the dll.