Can I use regular white sugar instead of powder sugar? I only have one cup of p. sugar and I have to get this cake done TONIGHT. Help...PLEASE!!!

No, you cannot substitute granulated sugar for powdered sugar directly.
However, you can make your own powdered sugar from granulated sugar using a BLENDER.

Run the granulated sugar through a BLENDER until it reaches the proper consistency. It is important to stir the sugar up from the bottom manually at least twice during the process to ensure all sugar is processed properly


taken from wikianswers.com