Pc for number crunching and large files

Hi all.
I am writing a PhD thesis in finance. I use very heavy excel sheets to host my market data and stocks information.
I need to build a pc that can crunch my numbers without the hassle of crashes.

let me give you an idea of what I have, what I do, and what i need.

I currently have the following gear:
PC, with intel Q9600 or so with 8GB ram but motherboard not very nicely working so i am getting it replaced. W7 installed and just installed office 2010. it seems to work correctly and pretty good.

my laptop is a macbookpro that runs very smoothly on excel sheets 2008 but, as a good microsoft product it does not support macros for macs.

My excel sheets are around 100MB each. so i need your advice on hardware AND software (OS system) to be able to build a pc that handles this load.
I am not very keen on gaming so i can live without it.

I was looking at some specs for AMD Phenom II X6 and the i7 930 to be installed with 64 bits os.
some smart guys here suggested to go to dual CPUs and server like structures that I have no idea how to handle. I feel that i need something to run like 16GB ram . my window 7 now does not see but 1.3GB of my 8GB installed and i am having this issue reviewed by some tech wiz around , with the possibility of replacing the MOBO which is an envidia 640 sli something but useless.

any suggestions?

many thanks

ghassan