Creating icons from some types of formats is easy in Windows, but the same in Mac is not just an easy task. Its better to have those icons from Windows converted into Mac icons. And there are a few tools that can help you with the same, and can also work in creating your own icons from images that you suggest.
Upload files from these formats and get the conversion done very easily with iConvert tool -
.icns, .ico, .png, .svg, .tif, .jpg, .bmp, .tga, .cur

With this free tool, you can convert Windows icons to Mac OS X icons, create your own buddy icons, emoticons, Windows XP icons, Mac OS X icons, and more. Simply upload a file in one of the specified formats, and iConvert will do the rest!

The process of uploading and conversion is very easy, and you can get the icons very easily and fast. Only the files from specified formats have to be uploaded. And these are for both Windows XP OS and Mac OS X.

You can check the tool at iConvert.