show BitmapImage in a picturebox

Question

hi
i have a program that is running on visual studio 2008 and i use some BitmapImage in that.
now i need to use this BitmapImage like a bitmap or jpg or etc that are normally usable in a picturebox.
i have some functions that their argumants are bitmap and i can't send them a BitmapImage as a argumant. so i can't use wpf because my program has some graphic functions and they don't work on wpf.

it's better for me to use the BitmapImage like a bitmap, any suggestion?

thanks in advance!