I have had this problem too. On Win 95 boxes when I want to print an invoice, I can do this:
set printer to name invoice
repo form invc to print
set printer to default

NT does not all name changes of network printers. You have to use UNC (universal naming convention) to address a network printer. My fix was to test which operating system is in use and set the printer accordingly.

if 'NT' $ os()
set printer to name \\server\shareptr
else
set printer to name invoice
endif
repo form invc to print
set printer to default

It may not be pretty, but it works