Do NOT run that downgrader, yes it will brick your psp if you attempted to downgrade any lower than 2.5 or thereabouts. This was an extra security measure sony added to ta-82 model psps, it has recently been hacked and ta-82s can now downgrade to 1.5 (and then upgrade to 3.03oe-a if you wish).
You need the
new 2.71 ta-82 downgrader.
Before the downgrader can run you will need to install
HEN-D (Homebrew ENabler version D). This patches the 2.71 firmware to allow (limited) unofficial code to be run, including the downgrader.
I STRONGLY recommend you join the psp-news.dcemu.co.uk or qj forums, read up on the downgrader and ask any questions you have in a forum with a lot of people who have used this downgrader already BEFORE you try to downgrade your psp.
Not knowing what you are doing and making a simple mistake can brick your psp.
You seem to be in a rush, dont rush to downgrade. Read everything you can about the downgrader before you go through with it.
You should have a decent general knowledge of computers too.