I have a large costing spreadsheet, and I want to be able to prevent people
from typing in cells that aren't appropriate. This has to depend on whether
a particular word in entered into another column.

So if column A had 'Forecast' entered into it, the user shouldn't be able to
enter anything into Columns G and H.

But if any other value is entered into the cell, they should be able to
enter data into G and H, but not F.

Is this possible with my version?