I actually did that, and was still confused.
You forgot to mention it.
You need the linux-headers package for this.
Edit: the linux-headers for your running kernel that is, not the one currently in [core]
]]># dkms install vboxhost/$(pacman -Q virtualbox|awk {'print $2'}|sed 's/\-.\+//') -k $(uname -rm|sed 's/\ /\//')
Error! echo
Your kernel headers for kernel 3.4.9-1-ARCH cannot be found at
/usr/lib/modules/3.4.9-1-ARCH/build or /usr/lib/modules/3.4.9-1-ARCH/source.
$ yaourt -S --force virtualbox-host-modules
resolving dependencies...
warning: ignoring package linux-3.6.7-1
warning: cannot resolve "linux>=3.6", a dependency of "virtualbox-host-modules"
:: The following package cannot be upgraded due to unresolvable dependencies:
virtualbox-host-modules
Do you want to skip the above package for this upgrade? [y/N] n
error: failed to prepare transaction (could not satisfy dependencies)
:: virtualbox-host-modules: requires linux>=3.6