Excel 2007 : How to automate calculation of threshold value?

Hi guys!

I am working on a pretty exciting project, and with the help of this forum and my own interest in excel, i have developed a very nice, easy-to-use spreadsheet for the project's rate of return.

The final challenge ahead of me: How to automate the calculation of threshold values for a number of parameters?

The challenge is this:

1. On input page, there is a table of input values.

2. After a number of calculations, the final sheet has an IRR value.

3. On a sheet called Sensitivity, I perform an analysis where I write the input value for each parameter at which the IRR value (final value) reaches a certain benchmark (threshold value)

Now, the calculations will likely undergo many many changes in the coming weeks, so I want to naturally automate this process?

Could you please tell me how?

Many many thanks!
s