New Use Syntax on Vista

No problem mapping using Windows Explorer to any of my partitions on my old
Dell running XP-home from my new Dell 546 running Vista Home Premium.
However would like to "automate" with a batch file. Historically have used
the syntax net use S: \\DELL8300\C mypassword. and T:\\Dell8300\D
mypassword, etc. Now get "system error 67" and "The network name cannot be
found." Rather surprising and frustrating since those are the names found
when mapping using Windows Explorer. Yes, if I check remap on boot that
works; but I would like to unmap at times and include the mapping
instruction in a batch file which will then perform other backup functions.
Appreciate some help. Have spent two days reading to no avail and eyes
grown dim.