How to generate dates as per australian working days automatically in excel

Attached document has 4 columns.

1. The first column(Date Submitted) is entered by manually.

2. The second column(QR Log Due Date) should be generated automatically by adding 20 working days to the first column.

QR Log Due Date (column B)= Column A + 20 working days (Australia)

3. Column C should have two options to select as follows:
1. Received
2. Not received
If I select received option, it should put the current day automatically as follows.

Received : 21/01/2011

4. Days Remaining (Column D)= QR Log Due Date(Column B) – Date Submitted(Column A) :only should consider working days

if the Days Remaining (Column D) value equal to zero or minus, the cell should flash in red colour other wise it should be flash in Green.

Please help me on this.

Please need a quick reply