You can read the full error messages by doing 'nano /var/log/XFree86.0.log'. The lines that are interesting start with (EE).
I remember someone in this forum pointing out a couple of days ago that there's a package called xdebconfigurator that can be installed to help in configuring X. Haven't tried that myself but it might be worth a try.
If you already have a working network connection, use 'su' command to get super user privileges and use apt-get or aptitude to install xdebconfigurator. Then do 'xdebconfigurator --help' to see how you can use that program.
If you haven't yet configured APT, you can do (as super user) 'apt-setup'. Also, you must update APT before you start installing packages. Either do (as super user) 'apt-get update' or run 'aptitude' and press the 'u' key on the keyboard. Aptitude is a GUI frontend for apt-get.
Also, you can do 'apt-get moo' to discover the Super Cow Powers of APT. (It's just a joke.)