COPY TO and VACUUM

Dear All

I'm running Postgres 8.4 on Ubuntu 10.4 Linux server (64bit)
I have a big table tath contains product information: during the day we perform a process that import new product
continouslywith statemtn COPY TO .. from files to this table. 

As result the table disk space is growing fast, it seems that postgres is not able to free space for old rows.

Is it possible to run a specific autovacuum acivity or say to postgres "every time I delete a row, delete it immedialty
anddon't take care of other transactions" ? 

Do you have any suggestion for me?

I'll appreciate every suggeestion you can provide me.

Many thanks in advance

Roberto