Quick! before everyone tells you their opinion of Pergo! Pergo isn't well received around here. I think it's a fine product for certain uses and budgets. Read some old posts (or wait for some new ones) about the pros and cons of Pergo.
..Back to your question: You can lay it right over the old floor - but you do need to lay the foam pad in between.
Also, if any of the tile is sticking way up, you may want to cut it out so the new floor lays flat. (A friend of mine once pulled up the carpeting in his apartment and found a baby bottle and a hot dog underneath... so that's what those bumps were! Amazing bit of laziness in that installation.)