Sequence and nextval problem

Hello everybody.
   I've got an vb aplication that uses an Access database. I'm trying 
to convert the database to postgres. The conversion was done ok, but 
i've got a little problem that i don't know how to solve. Let's see if 
anyone can help me.
   The conversion from access database to postgres worked fine. 
Everithing it's ok. But now, when i use my database i've found a problem 
with sequences. In the conversion, the "autonumeric" fields from access 
have been converted to sequences, everithing ok in a first view. The 
problem comes because the autonumeric fields in access always return the 
last value of the table +1, but postgres no. Postgres returns "lost" (i 
don't know how to call them) values. An example.
   This is an example of a table:
      code | description      ----- | ------------          1  | desc 1          2  | desc 2          6  | desc 6
  7  | desc 7
 

   In access if i execute "INSERT INTO table (description) VALUES 
('desc 8'), the result row is  8 |  desc 8   But in postgres the same query te result row is 3 | desc 8
   My question is, can i do something to make ANY sequence to take the 
last value from his associated table, and not a "lost" value?
   Thank you very much