Insert into large table

I am using version 7.3.1 on windows and am finding the insert/update performance on a particular large table is less than acceptable.

the table contains end of day share data and as such contain about 2000 entries for each day for the last 3 years.

At the end of each days trading I use the copy command to load the records into a temp table to check data validity then I use a insert into x ( ) select .... from temp

and wait and wait and wait.

My machine is a W2000 box with 256mb RAM and an Athlon 2000 processor so I expected a much faster result.

When I look in the task manager the postgres process is only using 2% to 6% of CPU time.

What things should I be checking to up the performance of the postgres DB?

thanks

Richard