Calculate after cell entry/auto filter change

I feel bad because this is my first post in the forum and its already about asking for help, sorry!. Never had any experience in writing VBA scripts so have not found any solutions/guides online that are coming to my aid.

[Problem]
I work in an IT department for a small company and one of my jobs it so solve random problems. The problem we have is that our finance department use excel 2003 for all there reports and tracking (they are finaly changing there system to opera soon). After nearly a year of inputing data onto there individual and joint excel sheets (some nearly 19mb) they are starting to respond really slow especialy when using the autofilters it takes ages to recalculate.

[Workaround]
I found a work around that involves turning off automatic calculation and pressing F9 to recalculate after the inputting has been done but the user (stubbon lady) does not want to do this as after she inputs a figure the cell next to it shows how much is outstanding.

[Question]
Would I be wrong in thinking a VBA script could be created to "press F9" after she has finished inputting into a cell? and to also calculate after the autofilter has finished filtering her choice?

Would anyone be able to recommend me guides so I can create this or to help me with example code that you have avaliable.

Yet again sorry to be asking for help on my first post but im stuck and trying to make a good impression in my 6 month contract so they offer me a permant job.

It sounds as though these files are heaped full of Volatile functions (or functions Volatile by association), and/or masses of expensive Arrays / Sumproduct formulae and perhaps Conditional Formatting ?

Altering calculation mode to Manual is IMO very much method of last resort - better to focus on the underlying cause of the slow calculation.

In answer to your question - yes you can use VBA to enforce a calculation upon a cell being altered whilst on Manual mode (see Worksheet_Change event) but I don't think that's really the best course of action... but to reiterate that's just m y opinion.

For more info. on Volatility and optimisation per se see the link in my sig.