Your frustration is understandable, but there's limits to what the NVIDIA installer can do to help you with the installation and configuration of the NVIDIA driver. It was designed to work as transparently as possible for as many users as possible, with the intention to remain distribution independent; it won't uninstall conflicting, distribution specific packages, it won't download and install development tools for your distribution if it finds them missing and it won't interface with distribution specific configuration mechanisms.
This is seen as a major shortcoming by some of the major distributors, but is the most reasonable approach considering the number of different GNU/Linux distributions alone. Distributors and users alike are welcome to redistribute the driver, to ship it with or repackage it for a given distribution; a number of distributors do this. SuSE chose not to, not because the NVIDIA software license prohibits it, but apparently due to legal considerations pertaining to the proprietary nature of the NVIDIA driver.
SuSE does provide documentation (Nvidia Installer HOWTO for SuSE Linux users
, linked to from the NVIDIA driver download page) detailing the process of installing the NVIDIA driver on different releases of its distribution, however, and you will find that it covers most of the difficulties you encountered. With respect to the login screen, I don't know what caused its change of behavior; the nvidia-installer
program doesn't modify display manager configurations.