How would I write a formula to produce various results in differant cells
based on a portion of a number in another cell. Excel 2003

Cell A contains a variable number.
Cell B also containes a variable number.
I need to calculate:
Cell C results need to be based on 1/3rd of Cell A x Cell B, if Cell A is
evenly divided by 3. This part is not a problem (B/(A/3). If Cell A can't be
evenly divided than: Cell A results need to be (B/(A/3) + 100% of cell B if
the remainder is "1" or 50% of Cell B if the remainder is "2" .

Than comes Cell D: This result needs to be (B/(A/3) + 0% if remainder is "1"
and 50% of cell B if remained is "2"

Than comes cell C: This result needs to be (B/(A/3) only on the hole number
result of A/3.