Macro to check for blank cell entry, copy previous value, and check for duplicates

Hi,
I hope someone can help me on this:
I have a workbook consisting of two sheets.

I need a macro button that will find every blank cell in column "B" of sheet 1, check if the value in the cell above exists on sheet 2, and if not then paste the whole row from sheet 1 into the next available row in sheet 2.

Any ideas, I'm totally lost with this one!