Internet Explorer vs Netscape Navigator
Differences between Internet Explorer (IE) and Netscape Navigator (NN)
These two major browsers are coming closer to each other regarding the DHTML effects possible towards newer versions. However you will need to remember that IE is more flexible than Netscape and due to small differences something that works really well in IE might not work at all in Netscape. So you need to be really careful and alert when programming for both browsers. One hint you can follow in most cases is that if you get it working in Netscape it should most probably work in IE.
Another major limitation of Netscape as compared to IE is that not all properties of a page can be changed at any time. This is because when the web page is once written to the screen, only position, visibility and clipping can be manipulated dynamically.
For Dreamweaver to not keep throwing up Netscape 4 errors set the browser check settings to show Netscape 6 instead of the default 4.0. To do this click on the Results panel, select the Target Browser Check tab, click on the green arrow to show the list of options - select the Settings option and set Netscape Navigator to version 6.0.