Die Anpassung muss in der httpd.conf des Apache stattfinden. Sollte im Ordner "\conf\" liegen.
Dort muss zum einen der Wert "DocumentRoot" und zum anderen die dazu passende Direktive <Directory "C:\xampp\htdocs"> angepasst werden.
So sieht es in meiner http.conf aus:
# DocumentRoot: The directory out of which you will serve your
# documents. By default, all requests are taken from this directory, but
# symbolic links and aliases may be used to point to other locations.
#
DocumentRoot "
d:\Web_root"
#
# Each directory to which Apache has access can be configured with respect
# to which services and features are allowed and/or disabled in that
# directory (and its subdirectories).
#
# First, we configure the "default" to be a very restrictive set of
# features.
#
<Directory />
Options FollowSymLinks
AllowOverride None
Order deny,allow
Deny from all
</Directory>
#
# Note that from this point forward you must specifically allow
# particular features to be enabled - so if something's not working as
# you might expect, make sure that you have specifically enabled it
# below.
#
#
# This should be changed to whatever you set DocumentRoot to.
#
<Directory "
D:\Web_root">
Alles klar?
Dunkel die eine Seite ist, sehr dunkel... Halts Maul Yoda und friss deinen Toast!