Okay, since no one answered this, and since it's embarrassingly high in a certain search on google, I'll answer it.
Gtk-WARNING **: Unable to locate theme engine in module_path: "pixmap",
Means you need to install the gtk2 pixmap engine, which usually comes with the rest of gtk2 engines. (if you had gnome installed, for example, you would already have them installed.
Instructions for the distros I've used.
apt-get install gtk2-engines-pixbuf
(While you're at it, install the rest: gtk2-engines-metal, gtk2-engines-lighthouseblue, gtk2-engines-spherecrystal, etc..)
pacman -S gtk-engines
If you don't want to install gnome AND don't want to mess around with the ~/.gtkrc-2.0 file, install gtk-theme-switch
Any themes you install should be extracted and placed in your ~/.themes/ directory so gtk-theme-switch can find themes.