Paste data into alternate blank cells

Hello, in using Microsoft Excel 2007,

I'd like to paste data from one column into a another column that has some data in it along with some blanks - but the trick is that the data being pasted from the first column into the second column can only fill in blanks in the second column! It should not overwrite any other data in that 2nd column

Example:

column1 - (column with data to be pasted - I'd copy this information)

A1 car
A2 bike
A3 motor-cycle

into column 2 below

D1 ford
D2 (blank row)
D3 10-speed
D4 (blank row)
D5 harley
D6 (blank row)

but the blanks would be filled in with the pasted data, the ending result would be

D1 ford
D2 car
D3 10-speed
D4 bike
D5 harley
D6 motor-cycle

(the rows assigned are just sample rows - not sure if rows and ranges MUST be givien to help with any formulas that may need to be created)