I am using blender to create models on Source, I think it's a good solution.
Here is a great tutorial to begin with, if you already know the basics of what a mesh is and few things.
http://cgi.tutsplus.com/tutorials/mode…art-1--cg-12763
It is a really useful tutorial because it gives you a lot of shortcuts and modeling methods. The problem with blender (and i guess other softwares have this too) is that there are tons of tools and shortcuts you need to learn, it's not as easy to begin as Hammer but way more powerful. Sometimes, you just have to go for it, introductions that last hours can be annoying and miss the point here : you want to learn how to do 3D models. Then, this T-rex tutorial is perfect for that, it's a complex shape (it's not just a table with 3 chairs around) but it's doable.
So i think that if you want to do models for Source, you should first try to learn one of the softwares (for example Blender, or 3DSMax, Maya ...), the export/compilation can be learned later.