"select for update" question....

Hello,

As I understand it:
Issuing a ³select for update² within a transaction will prevent other users
from modifying data. (exclusive lock)

I¹m contemplating using the DBI interface as a permanent client to postgres
for a group of users, and have a few questions.

Will the above procedure still exclusively lock the row, when using a
browser to issue a ³select for update²?
I¹m confused about sth->finish; and will it finish the transaction, before
the user re-submits the form data to update the row....

Can anyone help me or offer some ³howtos² to read regarding postgres and
DBI?

thanks.

Raoul.