Dates between Dates, If holiday then select this cell, If not select this cell, If em

Is there a formula I can use so I can fill dates down until a certain date eg start from 12th Dec 08 and finish 27th Jan 09.

Then can I use this in a formula eg so if cell a1 matches any of these dates then use a data if not use b data.

And finaly if b data is empty then select next cell in row if empty then next column until it finds filled cell