newbie questions

Hi all,
I've inherited some postgres databases and have a couple of questions
I'm hoping someone can help me out with.
First, is there a way to link the file in the database directory, which
are all numbers, to specific databases?
Second, I've got some dbs that have some really huge files. A nightly
vacuum (not full) is running. Several of the files have names followed by
rev numbers and are the same size; viz:
-rw------- 1 postgres postgres 1073741824 Nov 19 05:32 144287855
-rw------- 1 postgres postgres 1073741824 Nov 19 03:45 144287855.1
-rw------- 1 postgres postgres 1073741824 Nov 19 03:44 144287855.2
-rw------- 1 postgres postgres 1073741824 Nov 19 03:46 144287855.3
-rw------- 1 postgres postgres 1073741824 Nov 19 03:46 144287855.4
-rw------- 1 postgres postgres 1073741824 Nov 19 03:46 144287855.5
-rw------- 1 postgres postgres 1073741824 Nov 19 05:32 144287855.6
-rw------- 1 postgres postgres 12951552 Nov 19 05:32 144287855.7

This looks fishy to me. Is it? I know that there's no way that the db in
question could have 7gb of data in it.
I've been told that the way they've been getting the db back to a
reasonable size was via the ps_dump, drop table, recreate table psql <
dumpfile routing. Seems a bit excessive.

Can someone gimmie some advice please please please? Or point me to the
docs that'll clear up my confusion as I've not found them on my own.

-Mark