Windows XP introduced 32-bit icons for the desktop. Microsoft has some very detailed instructions on how to create 32-bit icons.
Unfortunately, as with many new technologies, there are some bumps along the road. One of these bumps is getting .ICO files to work well across all Windows platforms (so that the same icon looks as good as possible on both Windows 95 and Windows XP.)
Here are a few pointers that will help you out:
You can also use our ICONTEST utility. We wrote this application to quickly check the icons (without a development environment getting in the way.) You can download it here.
There is some documentation included in the download which was originally oriented at Mac designers who were new to developing for Windows. The documentation is a little bit out of date: the comments about not including a 16-color 48×48 icon doesn’t apply anymore (see the point above about getting the icon resources in the right order!)
We've tried to anticipate most questions you might have. However, if you can't find the answer you're looking for here, send us your query and we'll answer it personally.