Inserting VLookup With Variable Source Name With VBA?

I'm trying to create a macro that will open automatically generated report outputs and manipulate the data.

The macro will run from it's own workbook (Report Macro.xls), sheets / cells within this workbook are available as 'helpers'.

So far what I have working ok is;

Via a browse dialogs in a userform in Report Macro.xls I select 5 different report outputs. I'm storing the full filename & path in Sheet Data, Cells B1:B6 (B1 being the filename & path to the macro file). In column C I have just the filename

The first file is opened and manipulated as required. The next thing I need to do with it is to open the second file (filename / path in B3) and put a Vlookup in cell 02 of the first file which will look for data in the second (the second file will only ever have a single sheet).

As a formula I'd be using

Code:
=VLOOKUP(A2,'Email 22FEB12.XLS'!$B$7:$C$13120,2,FALSE)
In VBA if I use;

Code:
ActiveCell.FormulaR1C1 = "=VLOOKUP(RC[-14],'Email 22FEB12.XLS'!R7C2:R13120C3,2,FALSE)"
It works great. However, the second filename will change and I need to take it from the macro file, sheet 'Data', cell 'C3'.

How can I use the contents of sheet Data, cell C3 in the VBA code above instead of the filename being hard-coded?