Question: When you run "pacman -S nvidia-304xx", are you running from the GUI environment? If so, the libraries listed in
[root@archbox iceman]# pacman -S nvidia-304xx
looking for inter-conflicts...
:: nvidia-304xx-utils and mesa-libgl are in conflict (libgl). Remove mesa-libgl? [y/N] y
error: failed to prepare transaction (could not satisfy dependencies)
:: ati-dri: requires mesa-libgl=9.2.0
:: glamor-egl: requires mesa-libgl
:: intel-dri: requires mesa-libgl=9.2.0
:: nouveau-dri: requires mesa-libgl=9.2.0
may be in use, which I would expect to generate error messages.
On the other hand, is you run "pacman -S nvidia-304xx" from text mode (from runlevel 1 or 3), there would't be any conflict with GUI graphics.
Try installing the nvidia driver from text mode. When installation is complete, exit root to user, then startx. That should get you to GUI with the nvidia driver.
I hasten to point out that I have never used Arch. I'm relying on my experience installing nvidia drivers in other distros.