Transactions, PostgreSQL and MS Access front end.

From Access I'd like to run pass the following from MS Access to
PostgreSQL 8.1 using VBA:

BEGIN;
UPDATE accounts SET balance = balance + 100.00 WHERE acctnum = 12345;
UPDATE accounts SET balance = balance - 100.00 WHERE acctnum = 7534;
COMMIT;

It won't let me.  Any ideas solutions?