Undo any permanent changes you've made using the tar file installation. Normally I'd suggest using tar files, but in this case, they're giving you strange errors, so don't bother.
The "failed to initialize" message you got with the RPM drivers almost always means your drivers are installed properly, but the kernel module (NVdriver) isn't getting loaded.
If you're booting to a text-mode login, try doing a /sbin/modprobe NVdriver (as root) before you try to startx -- that should fix it until you reboot. After a reboot, it's a bit of a different story. It is fixable, but the fix depends on whether or not your distro runs devfs. To find out, run one of these:
[ -c /dev/.devfsd ] ; echo $?
If it prints a 0, then edit your /etc/modules.conf file and add a line reading alias /dev/nvidia* NVdriver
It it prints a 1, then edit your /etc/modules.conf file and add a line reading alias char-major-195 NVdriver
When you're done, do a depmod -a as root, and reboot to see if it works (actually, rebooting isn't strictly necessary, but it's easiest).