Two things:
1) I always add the word nvidia to /etc/modprobe.preload otherwise the nvidia module that you just installed for video accelleration does not get loaded at boot time and you end up using the original nv module (unaccellerated). This is what my modprobe.preload file looks like, also has a couple other modules listed but I left them out as yours may differ. Note: this is incase you find you are still using the old video driver, not actually directly related to your question.
Code:
# /etc/modprobe.preload: kernel modules to load at boot time.
#
# This file should contain the names of kernel modules that are
# to be loaded at boot time, one per line. Comments begin with
# a `#', and everything on the line after them are ignored.
# this file is for module-init-tools (kernel 2.5 and above) ONLY
# for old kernel use /etc/modules
nvidia
2)Open up Mandrake Linux Control Center, highlight the "Boot" tab, and click on "Enable autologin and select the user to automatically log in"
You should have an "x" in the box "Launch the graphical environment when your system starts"
and choose which user and desktop you want auto launched.