Restricting access to rows?

We have a growing ASP-hosted application built on PHP/Postgres 8.1, and are
getting requests from clients to manipulate the databases more directly.
However, the structure of our databases prevents this from happening readily.

Assume I have two tables configured thusly:

create table customers (
    id serial unique not null,
    name varchar not null
    );

create table widgets (
    customers_id integer not null references customers(id),
    name varchar not null,
    value real not null default 0
    );

insert into customers (name) values ('Bob');
insert into customers (name) values ('Jane');
insert into widgets (customers_id, name, value) VALUES (1, 'Foo', 100);
insert into widgets (customers_id, name, value) VALUES (1, 'Bar', 50);
insert into widgets (customers_id, name, value) VALUES (2, 'Bleeb', 500);

This leaves us with two customers, Bob who has two widgets worth $150, and
Jane with one widget worth $500.

How can I set up a user so that Bob can update his records, without letting
Bob update Jane's records? Is it possible, say with a view or some other
intermediate data type?

Thanks,

-Ben
--
"The best way to predict the future is to invent it."
- XEROX PARC slogan, circa 1978