What version of X did it install? I had the same error for a pretty substantial amount of time when I didn't have it configured correctly for my hardware.

What I would recommend is as follows : (if you have version 4.2.0 or later, then jump to step 3)
1. get the latest version of X. See the details on the latest releases http://www.xfree86.org. It is free for download at many locations. I have always had good luck on the mirror ftp.rge.com. [you are likely to be asking why get the latest version, and I say because it is easier to configure. You'll see in a bit.]
2. once you have the latest version, run "sh ./Xinstall.sh" and install the software as needed.
3. once the software has installed, you will want to run "XFree86 -configure" and this will create the file /root/XF86Conf.new and you merely need to move it to the correct location for your system. (This is the reason I recommend getting the latest version, it will probe and configure for system and you can move the file to whatever location it belongs.)
4. Ensure you have the file $home/.xinitrc and that it points to your window manager of choice. Sample of mine is as follows :
Code:
exec enlightenment
I believe the commonly used lines for the file are gnome-session or startkde for Gnome and KDE respectively.

Hope this helps and best of luck.
Regards.

[edit]
I should let you know that the commands and locations of files vary based on distro and *nix variation. Most of the information I have provided is more oriented to the BSD's, but all the concepts are the same with minor modifications. I believe that this is likely to be of value to you as well. ProblemChild provides some Linux distro specific details.