fatal error configuring Xorg on 5.3

[Mario Hoerich]

# dave:
> Fatal server error:
> xf86EnableIO: Failed to open /dev/io for extended I/O

It seems you don't have the modules io and/or mem loaded.
Check with 
  # kldstat
and load whatever's missing with
  # kldload [io|mem]

Does this solve your problem?

You might want to just add 'device io' and 'device mem' to
your kernel config.

Cheers.
Mario