Retrieving PK of inserted row

I want to retrieve the primary key, which is a SERIAL, of a row I just
inserted.

In 8.2, I could use RETURNING, but I'm using 8.1.

Reading around, I've seen the following methods discussed:
(1) Within a transation, do the INSERT, and then do a SELECT CURVAL
(2) Not necessarily within a transaction, get a candidate for the pk using
SELECT NEXTVAL, then INSERT the row.
(3) Use LASTVAL

My questions:
* Are any of these methods flawed?
* Is there any reason to prefer (1) to (2)?
* I'm not sure whether LASTVAL is guaranteed to work outside of a
transaction.  Its description in the 8.1 manual starts with "Return the
value most recently returned by nextval in the current session. ..." but I'm
not sure of the formal sense in which "session" is being used.  (I'm
connecting to the DB from mod_php in apache, so I guess "session" could mean
"during the existence of a given db connection," but I'm not sure.)

TIA