XFree86 4.0 does not yet use Xwrapper and the XFree86 binary is not installed suid root. Therefore, X can't be started by a normal user from the console via startx.
Note that this first causes the error about not being able to write the log file in /var/log, but even if you make that writable, you still need to suid X so that it can open the console
*** Bug 12024 has been marked as a duplicate of this bug. ***
I would like to add my vote to the return of Xwrapper, XF 40 works fine with it just set /etc/X11/X to point to /usr/X11R6/bin/XFree86, and it is a must for the 3.3 servers.
*** Bug 12134 has been marked as a duplicate of this bug. ***
confirmed in beta2
This bugs seems almost fixed in the just released 0.29 snapshot of Xfree: XFree86-4.0-0.29 There is an correctly installed xwrapper now, but XFree86 itself also is suid root (bad !) and the 3.3 servers like XF86_SVGA have standard permissions, while they should be exute only (no read) by group and other, for safety reasons.
This should be fixed in 0.30; fully functional Xwrapper should be included.