I second everything that gotwood said, except leaving the pad. Well actually, the pad is a great place to roll up tackstrip, but it will be easier if it's not in the way at the edges. Remove it, so you'll have room to slide/slam the scraper into/ underneath the tack strips.
And pay attention. Locate the tackstrip nails( every 6" or so) and use leverage AT the nail.
Alot of times it'll pop up with nail still in it.
If you pry in between nails...it's likely to break and then you still have to pull the nails and the little pc. of tackstrip that will still be there.
Also..I use a pry bar and slam it under at the nail then pry.
This may hurt you mere mortal hands and will cause blisters. But stick with it.