I am looking for a way to fill a number of cells in a row/column based
on a particular cell's value. So, if a cells value is say 7 or 3, then 7
cells or 3 cells must be be filled with a particular colour.

In my example, cells of column A are filled in based on the value in cell C1.

Select column A and use "conditional Formatting" with "use a formula". The formula is
=ROW()<=$C$1
Choose the format and click OK.

With Excel 2010, when I update C1 the filled rows don't change (for some reason) until I select column A.

Hope this helps getting started.