SUBST [drive1: [drive2:]path]
SUBST drive1: /Ddrive1: Specifies a virtual drive to which you want to assign a path.
[drive2:]path Specifies a physical drive and path you want to assign to a virtual drive./D Deletes a substituted (virtual) drive.
Links:
[1] http://linux.philosweb.com/drupal5/files/rtelnk_2_4.gif
[2] http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/subst.mspx?mfr=true