When you create an HTML frameset using the FRAMEBORDER="0" attribute, the frames look fine in Internet Explorer. However, there's an unsightly white gap between non-white pages when you view the frameset in Netscape Navigator. That's because Netscape doesn't support the attribute. Instead, it wants to see BORDER="0" to do the same thing.
Here's an example of a frameset that looks right in both major browsers:
<frameset cols="20%,*" BORDER="0" FRAMEBORDER="0" FRAMESPACING="0">
<frame Scrolling=No SRC="menu.asp" Name="menu">
<frame Scrolling=No SRC="main.asp" Name="main">
When rendering HTML tags, browsers generally ignore attributes that they don't understand.