Eric
On both of our Windows installs the backslashes are the conventional DOS backslahses - as suggested in the config-dist.php file. So I have
$CFG->dirroot = 'c:\apache2\htdocs\moodle';
However, here is the anomaly:
$CFG->dataroot = 'f:\moodle\/moodledata';
Notice the forward slash infront of 'moodledata'. So Darren's $CFG->dataroot should read
$CFG->dataroot = 'C:\Inetpub\vhosts\mrahos.net\httpdocs\/moodata';
But, re Howard's point, it should be outside the $CFG->wwwroot path for security 
.
Ken