If you want to make those big, snazzy desktop icons for Windows Vista but don't want to fuck around with shitty, bloated software like Axialis IconWorkshop™ then I highly recommend this website:
It's a free, quick, easy website that converts PNG files into icons and vice versa.
How to use it:
1. Make a 256x256 PNG image in your favorite image editor
2. Go to http://converticon.com/
3. Click "Browse" and select your image (make sure you choose PNG in the dropdown box)
4. Click "Export". For Windows Vista, check all of the boxes in the left column
5. Click "Save as..."