Microsoft gave Excel a major facelift with its introduction of Excel 2007. Depending on which version you have, there are different options available for formatting numbers in Excel. I'll go over the universal step first and then cover some of the other ways to do this.
Format Numbers in Excel
In order for Excel to show negative numbers in parentheses, you have to instruct Excel to do so. This is done in the "Format Cells" dialog. No matter which version of Excel you have, you should be able to quickly access this dialog box by selecting the cell or range of cells that you want to format and then right-click on Format Cells. This will open a dialog box with the following tabs: Number, Alignment, Font, Border, Fill, and Protection. Obviously, you will want to use the Number tab.
In the Category section, click on the type of number you are working with such as number or currency. Since you mentioned currency in your question, let's look at currency as an example. Once you select currency, you'll see the main part of the pane now displays several options. It shows you a sample and provides you with three editable fields: decimal places, symbol, and negative numbers.
Select the number of decimal places you want to display. If you select 2, then the numbers will display two decimal places such as £50.00 whereas if you select five decimal places, the numbers will look like this: £50.0000000. If you want to change the currency symbol from £ to $ or even ¥, do so in the Symbol field.
Finally, the answer to your question lies in the next field, negative numbers. You have four choices for displaying negative numbers:
£50 (red text)
(£50) (red text)
Choose the third or fourth option to place your negative numbers in parentheses. If you want your negative numbers to be displayed in red text, choose the fourth option.
Format Numbers in Excel 2003
While it's easy to simply right-click a set of numbers, Excel offers other ways to access the Format Cells dialog. If you have Excel 2003, select the cells you want to format, go to the menu bar, and click on Format > Cells. From there, follow the above directions to format your numbers.
Format Numbers in Excel 2007
Excel 2007 does not have the handy menu bar. In its place is the infamous "ribbon." You must have the Home tab active and then find the area of the ribbon labeled "Number." A drop-down box allows you to quickly change the basic number type such as from General to Currency. However, if you want to change the way negative numbers display, you'll need to click on the tiny square found in the lower right corner of the Number section. This will open the Format Cells dialog box.