Issues with Viewing navigation design

Hello! I created this website, www. sinforcharity. com/new-website/home.htm, in Dreamweaver. The top navigation bar should be one continuous line of color from the wings fading to white as it reaches the right side of the screen. When I view it on my computer in Internet Explorer 8, it looks fine. However, when I view it on my friend's computer (IE8) or my husband's computer (IE7), it's broken in to squares and sometimes the boxes are lower than they should be. Any ideas on what I need to do to fix this? Why would it look different on two computers, but in the same version of IE? What do you see?