A little advice on head modification?

Alright, well, my goal is to create or edit an existing head model and attach it to a body model to make a new playermodel - however I have no idea how to go about this.
What software would you recommend I use? I have ZBrush, XSI Mod Tool and Blender. I have to tools for texturing, and I have a rough idea of the Lua that would go into it. But as for the actual path to take…
Well? What do I need to do to create/edit the original head model in ZBrush/Blender/XSI and what are the steps to exporting it for use in the Source engine?

Any and all help is much appreciated.

Come on, there has to be someone out there who can help :frowning:

http://www.facepunch.com/showthread.php?t=939746

[editline]10:26PM[/editline]

I would probably go with XSI Mod Tool out of those.