Serious Excel 2007 speed/formula issues!

Hi all,

I'm working with a large spreadsheet - by my standards - (~50MB), it has 12 tabs containing various data sources that should contain similar inventory information, and one tab that has the original data on it, and I am adding any new information, also performing lookups to the other data sources as a comparison.

I have a couple of examples of the formulas in use:

The first one is to identify if a name on the original sheet exists in another data source, and if so to put an "a" in the cell (to be text formatted as Marlett and show a tick):
=IF(ISNA(VLOOKUP(B2,Data_Source!$A$1:$A$100000,1,FALSE)),"","a")

The second is to identify if a name on the original sheet exists in another data source, and if so to display various attributes that the name has against it:
=IF(ISNA(VLOOKUP(B2,Data_Source!$A$1:$B$100000,2,FALSE)),"",VLOOKUP(B2,Data_Source!$A$1:$B$100000,2,FALSE))

The issue that I have is that Excel is taking anywhere between 10 and 15 minutes to perform the calculations on this and it is becoming unworkable. I have tried turning off automatic calculations, but that just delays the inevitable...

I've been trying to find a different formula that will produce the same results as VLOOKUP as the results I am getting are exactly what I need. The formula that I have found to use is INDEX-MATCH, only thing is that I'm having trouble figuring out how this would be used in the context of my original formulas.

Does anyone have any thoughts/suggestions, and help would be greatly appreciated!!

Thanks

Adam