Unprotecting Cells By Date Change

[greasyfingers]

My spreadsheet has a column for the date, progressing down the rows, and another column for an amount. Like this:

|_____A____|____B____|
|___Date___|_Amount__|
|_1 Nov 08_|_________|
|_1 Dec 08_|_________|
|_1 Jan 09_|_________|
|_1 Feb 09_|_________|
|_1 Mar 09_|_________|

The cells in column B all contain a formula, and are protected, such that cells in that column appear blank for all dates in the future, but as they become current a number appears according to the formula in the cell. This number may need to be overwritten.

So once the date in A <= today's date, I want the adjacent cell in B to become unprotected (and change background colour).

Is this possible? I was hoping that I could do it with Conditional Formatting, but I can't figure how to change the format of one cell depending upon the condition of another.