Vista Style Builder

I am using VSB with Vista SP1 and was experiencing the exact symptoms you describe. Simply saving a copy of the Aero style wthout making any edits would cause the themes applet to crash. I also experienced the login issue.

I found the solution had already been given in these forums. Try the following:

In %AppData%/VistaStyleBuilder/Settings.ini, add the following setting:
  [Settings]
  FirstImageId=1

This resolved the issue for me, I can now edit and save my styles. Hope this helps.