Formatting Excel (.xls) for 2 decimal places

I was creating a spreadsheet today to help me calculate the running costs of an eBook that I’m writing for a client. It’s a bit complex so I’ll leave the details for another day…

In any case, I couldn’t for the life of me figure out how to change the decimal in my cells over to two decimal places. I found instructions for Office 2003, but I’m using Office 2007 and the setup is completely different.