What desktop are you using? You will have to modify your /etc/rc.conf file:
Code:
# What display manager do you use ? [ xdm | gdm | kdm | entrance ]
DISPLAYMANAGER="kdm"
.....
XSESSION="kde-3.3.2"
That is a sample from my file - tailor your own file as you see fit.
Then if you issue the command (as root):
Code:
# rc-update add xdm default
then reboot, KDM should come up as your graphical display manager.
Of course this all depends on Slackware being similar to my system (which is not slack) - others can advise if the above method is not suitable for your distribution.
Regarding your resolution, you can either manually change it in your /etc/X11/xorg.conf file, or you can do it more or less automatically (how much automation depends on which method you choose) with a utility. Have a look at this to get some ideas.
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