|You can also use Conditional Formatting to "light up" all the values that are negative.|
Select all your data in their columns,
don't select the whole column, just the cells with data in them.
This is for 2007:
On the Ribbon,
Click the Home tab
Click Conditional Formatting
Select Highlight Cell Rules
Click Less Than
In the "input box" enter Zero
All your values that are Less than Zero will be colored.