I customize the Mozilla Firefox icon with Alucard's hellhound form, to complete my Hellsing IconPack!!
1 .ico file, for Windows XP & up. Png file also available here: [link]
To change applications icons:
Right + Click the application icon you want to change and choose Properties
Choose the tab Shortcuts.
Click on Change Icon to open the window for changing the application icon.
Here you have a choice to either Browse to a folder containing any .ico files or Select an Icon from the List shown containing default Windows icons.
Once you have selected an icon as described in C click OK.
Click on Apply.