background-position: is a property in CSS that places the background image inside the element to where you need it to be. If you do not want it to repeat for example, but you want it in a specific place… It’s kind of like position as in you use top/left positioning within it.
Have a look here for more info and examples: http://w3schools.com/css/tryit.asp?file … e_position
As for the image transparency – no. IE6 wont support alpha transparent PNGs. You either need to use the fix or create a GIF alternative. Personally I would use the fix. :)