You're running NTFS on your Windows drive, then, right? If so, you won't be able to make it writable -- Microsoft changes the filesystem format too often for the drivers to be stable enough that you won't run the risk of hosing your entire Windows partition if you enable write support.
Anyway, if those are the permissions (and not -rwsr-xr-x instead), then it's probably that your XFree86 binary needs to be installed suid root so that it can use your hardware correctly (not to mention so that it can write to /var/log). Either that, or it needs to be run as root, from xdm or gdm or kdm, but it sounds like you don't want to use those. So try (as root) doing a chmod u+s /usr/X11R6/bin/XFree86 and see if that helps.