If we slip up and finish 6thwith Portsmouth finishing 5th and win the FA Cup - then 6th would be good enough for UEFA cup entry. 
I didn't actually think that would happen, but according to BBC;

I didn't actually think that would happen, but according to BBC;
Should a team finishing in the top four in the Premier League win the FA Cup (still technically possible in Portsmouth), the Uefa Cup place would go to the team finishing sixth in the league.
If Portsmouth win the FA Cup and finish fifth in the Premier League, the sixth-placed team in the league would enter the Uefa Cup, not the FA Cup runners-up.