Storing a youtube video

Hey Gang,
I dont get this deal why they wanna do it this way but lets see if I can explain..I want to put a video on a site but it requires it to be in flv,wmv,asf,avi,mpeg, mpg the list goes on
THEN , it has a "browse window" that goes to my computer file registry for me to choose a file...Now, how do I turn a you tube video into a file I can store in my computer...Anyone ever have to do this?..Could someone please explain this process..
Thanks,
John
I dont get this deal why they wanna do it this way but lets see if I can explain..I want to put a video on a site but it requires it to be in flv,wmv,asf,avi,mpeg, mpg the list goes on

Thanks,
John