Need help with coding in VBA for Excel 2007

I'll try to make this as short as possible...

I have a workbook called "Modifications" which consists of two (2) worksheets called "Mod Calcs" and "Formulas".

The "Mod Calcs" sheet contains a cell (N13) which uses VLOOKUP to find a specific formula on the "Formulas" sheet.

The formula referenced on the "Formulas" sheet is a function of user-inputs from the "Mod Calcs" sheet. Therefore, I need the formula on the "Formulas" sheet to reference, and pull values from, the active row on the "Mod Calcs" sheet.
I can't figure out any "in cell" formulas to do this so I'm assuming I'll need to use VBA coding...

Here is the Psuedo-Code (for a specific row):
-------------------------
'Mod Calcs'!N13 = VLOOKUP(B13,Formulas!A4:F27,4,FALSE)

'Mod Calcs'!N13 now references Formulas!C9

Formulas!C9 = 'Mod Calcs'!C13*'Mod Calcs'!D13
--------------------------

Can anyone write an example of what this code would look like?
P.S. I understand that it may be easier in FormulaR1C1 format...

I do NOT want the calculations/formulas/references to be hard-coded (i.e. $a$1). That way I can repeat the formats & formulas over a range of rows with each row's calculations being independent.

Thanks in advance,