Error when using webform

I'm reasonably new to Drupal and I'm working my way through a few things so I may have missed something but...

I enabled webform having run the postgres script and all is OK. So I then went to add content (create content ->webform) the page loads but there's a PHP error as follows:

warning: pg_query() [function.pg-query]: Query failed: ERROR: syntax error at or near "FROM" at character 13 in /web/drupal-4.6.2/includes/database.pgsql.inc on line 45.

user error:
query: SHOW FIELDS FROM webform in /web/drupal-4.6.2/includes/database.pgsql.inc on line 62.

I ignored the error and carried on to see what would happen - I filled out the bits on the form and submitted it to get the following:

warning: pg_query() [function.pg-query]: Query failed: ERROR: syntax error at or near "FROM" at character 13 in /web/drupal-4.6.2/includes/database.pgsql.inc on line 45.

user error:
query: SHOW FIELDS FROM webform in /web/drupal-4.6.2/includes/database.pgsql.inc on line 62.

warning: pg_query() [function.pg-query]: Query failed: ERROR: column "email_from" of relation "webform" already exists in /web/drupal-4.6.2/includes/database.pgsql.inc on line 45.

user error:
query: ALTER TABLE webform ADD COLUMN email_from varchar(255) in /web/drupal-4.6.2/includes/database.pgsql.inc on line 62.

warning: pg_query() [function.pg-query]: Query failed: ERROR: column "email_subject" of relation "webform" already exists in /web/drupal-4.6.2/includes/database.pgsql.inc on line 45.

user error:
query: ALTER TABLE webform ADD COLUMN email_subject varchar(255) in /web/drupal-4.6.2/includes/database.pgsql.inc on line 62.

warning: Cannot modify header information - headers already sent by (output started at /web/drupal-4.6.2/includes/common.inc:384) in /web/drupal-4.6.2/includes/common.inc on line 192.

After which I decided to get some advice... I'm running Apache 2 / PHP 5 and Postgres 8 on Debian if that helps. I would really apreciate a steer on this as I'm really sold on Drupal in every other respect.

Many thanks

Nick