sorting big tables :(

I think soon people are going to start calling me Mr. Big...Tables...

I have a big table. 40M rows.
On the disk, it's size is:
 2,090,369,024 bytes. So 2 gigs. On a 9 gig drive I can't sort this table.
How should one decide based on table size how much room is needed?

Also, this simple table consisting of only 2 int4 values is the exact size
of an equally sized table consisting of only one int2. There seems to be
too much overhead here. I realise there are extra things that have to be
saved, but I am not getting the size/performance I had hoped for... I am
starting to think this segment of the database would be better implemented
without a dbms because it is not expected to change at all...

-Mike