You hit on the biggest problem on the internet, different browsers see things differently. But here are a few hints to keep things consistent.
Only use simple fonts (Ariel, times new roman, etc.) Dreamweaver comes with only 6 fonts as standard, stick with those.
Don't us layers. Netscape has a real problem with layers (specifically the div tag).
Keep styling of fonts to a minimum and use CSS. If you need a fancy headline or other font use, better to do it as a graphic.
Make sure that your graphics are created at the correct size for where they are placed. Don't resize graphics in Dreamweaver, do your resizing in Photoshop then put them on your web page. Some browsers will not see the Dreamweaver resize and will show the graphic at its original size. So make the original size correct. You should be doing this anyway.
The reference files in Dreamweaver have good information on which browsers support what. If you are using Dreawmweaver 8 look in the Window menu and click on Reference. Dreamweaver MX and MX 2004 have reference in the panels on the left.
So, bottom line, keep it simple. Use only simple fonts. Don't use layers for anything important, or for layout (I always use tables). Do all your fancy stuff with images. Or if you want a perfectly controlled web site that views identically in all browsers build the whole thing in Flash (but you will lose your search engine compatibility)
And don't forget that all of the browsers let the user customize how they work, including how they handle fonts. So even with your best efforts there will be people who will see your page layout differently than you designed it.