actually...made a small breakthrough with what you've got there

=IF(A1="A",IF(B1>100,"atrueover","atrueUnder"),IF(A1="B",IF(B1>100,"btrueover","btrueunder"),"Neither"))

what this is doing is looking at cell A1 and asking if that cell equals "a" if it does it then checks cell B1 to see if it's over 100..if it is..it returns "atrueover", if it's not it returns "atrueunder") if A1 ISN'T = "a" then it asks if A1="b" if it is then it asks if b1 is > 100..if it is then it returns "btrueover" if it's not then it returns 'btrueunder"...if A1 is neither A nor B then it returns "neither"

to test this you can make a spreadsheet..within the spreadsheet you'd endup with the columns being

columnA | ColumnB | Column C |

A | 100 | <formula>|

B | 75 |

C | 1000 |

then you would drag the formula down from C1 to C3 which would make the data look like this

columnA | ColumnB | Column C |

A | 100 | atrueunder |

B | 75 | btrueunder |

C | 1000 | neither |

to make this work for you...you would need to make the "atrueunder" and the like into whatever calculations you want such as

=IF(A1="A",IF(B1>100,d1*2.5,d1*3),IF(A1="B",IF(B1>100,d1*5,D1*7),"Neither"))

wich would make your data look like this

columnA | ColumnB | Column C | Column D |

A | 100 | 3 | 1

B | 75 | 14 | 2

A | 25 | 9 | 3

B | 250 | 20 | 4

C | 1000 | neither | 5

if any of that makes sense