Timezone Conversion

Hi

I am totally new to VBA EXCEL and trying to understand it but i got stuck at one problem.
I am using Excel 2007.

My problem is regarding conversion of timezones(GMT, EDT, IST etc).
i have cells B1 to M1 with names of timezones and B2 to M2 with their time differences w.r.t GMT
GMT is put up in B column
i know the formula used for conversion if GMT is fixed and all other rows are changed according to its value.
Formula is: (for C3 value)
=MOD($B$3-(C2/24)*-1,1)
But i want the values to change depending upon any value.
ie if we are changing any cells value , it should adjust all the other cell's values in that row
and also if user is entering any new cells entry say for IST, other cells should also get filled as per

i have attached my excel file for rows and columns.

i have searched a lot but nothing found.
Any help would be appreaciated.

Thanks