Subdomains on Plesk - (THis was taken from Plesk support forum)
k you go in into new domain and you do everything BUT, make sure you UNCHECK the WWW option, then just type int he sub you want example. If you leave the WWW option enabled, everytime you go to the URL of the SUb you will be automatically refreshed thru your browser and then see the URL change to the sub but, with a WWW in front of it.
sub.domain.com <<== replace sub with name of subdomain.
Valuablehost - PLEASE, sometime soon. I don't care for the transfer of my files, I just want access to my site...