IF Condition to date cells with concatenation of two text cells

Hello All,

I'm trying to automate an excel sheet. Sheet1 contains 4 columns and n rows.
4 Columns = A, B, C, D. Columns A and B have data(text) in them. Columns C and D have dates in them.
D cell can be empty without a date but C wont. Now the requirement goes this way:

If D has a date, Concatenate A and B and paste the data under Column of corresponding month(current year)
Else
C's date, consider it, concatenate A and B and paste the data under Column of the month(current year).

This is the requirement. Any help appreciated.

Regards,
D

A	B	C	D
Data with text	Data With Text	dd/mm/yy	dd/mm/yy(this column will be empty most of the times)
Data with text	Data With Text	dd/mm/yy	dd/mm/yy(this column will be empty most of the times)
...	...	dd/mm/yy

result:

Jan	Feb	Mar	Apr
Concatenated data of Cells A and B with their C/D dates falling under Jan/2013	Concatenated data of Cells A and B with their C/D dates falling under Feb/2013	Concatenated data of Cells A and B with their C/D dates falling under Mar/2013	Concatenated data of Cells A and B with their C/D dates falling under Apr/2013
Concatenated data of Cells A and B with their C/D dates falling under Jan/2013	Concatenated data of Cells A and B with their C/D dates falling under Feb/2013	Concatenated data of Cells A and B with their C/D dates falling under Mar/2013	Concatenated data of Cells A and B with their C/D dates falling under Apr/2013
Concatenated data of Cells A and B with their C/D dates falling under Jan/2013	Concatenated data of Cells A and B with their C/D dates falling under Feb/2013	Concatenated data of Cells A and B with their C/D dates falling under Mar/2013	Concatenated data of Cells A and B with their C/D dates falling under Apr/2013

....