Question : Creating the perfect icon

I have created an appliction that will be installed onto low end PCs running XP to high-end Windows 7.  I have created an icon within Photoshop CS3, which is currently set at 256x256.  I could really do with a hand creating the correct format of icon (with transparency).

I have come across several programs which work as plug-ins, but I could really do with some advice as to the sizing and best practices.

Any help would be greatly appreciated.

Answer : Creating the perfect icon

Yes it will based on a number of factors such as user preferences.

Just make sure that you include the appropriate sizes right down to the small ones (if you need Start Menu icons too).  These are all listed here -> http://en.wikipedia.org/wiki/ICO_%28file_format%29