Data validation help

I think its data validation I need.

I am developing a sheet which will have the info entered into across
the page. There will be lots of rows of info entered on this sheet.
Each row will need the same rules.

The user will need to select the currency e.g. GBP if its GBP they
will be able to enter info into certain cells but not others. Also if
its non GBP there is another cell that will need to be entered into
and cells I won't want entered into.

Is there any way I can set up some rules to do that.