Table transform query

Hi,

I'm trying to find out how to transform this kind of table data (history
of rental data in a firm):

date serial delivery
----------------------
1 1 L
1 2 L
1 3 L
2 1 R
2 2 R
2 4 L
3 5 L
3 3 R
3 4 R
4 1 L

... into this:

serial dateL dateR
--------------------
1 1 2
1 4
2 1 2
3 1 3
4 2 3
5 3

Basically, data on table 1 means:

- on date 1, product with serial 1 is sent to the customer
- on date 1, product with serial 2 is sent to the customer
- on date 1, product with serial 3 is sent to the customer
- on date 2, product with serial 1 comes back
...

On table 2, data means:

- Product with serial 1 is sent to the customer on date 1, and comes
back on date 2
- Product with serial 1 is sent to the customer on date 4, and hasn't
come back yet
...

Do you think there is a generic SQL solution to this problem, like
crosstab or pivot table?

I'm thinking of doing things in a "procedural" plpgsql manner...

Any idea is welcome.

Thanks!

Philippe