OK - so this particular page in question uses frames to accomplish what you're wanting...for IE, it uses the <iframe> tag and for Netscape it uses a function called "MM_openBrWindow" as evidenced by this snippet of code (the function itself is the 7th one from the top in the javascript in the head section):
<td width="190" class="sidebar" valign="top">
<p class="mediumheading">explore...</p>
<iframe src="portfolio/menu.htm" name="NewsFrame" width="98%" height="120" align="default" frameborder="0">
<p><a href="#" onClick="MM_openBrWindow('portfolio/nsframeset.htm','nnportfolio','scrollbars=yes,resizable=yes,width=600,height=360')" onFocus="if(this.blur)this.blur()"><img src="images/misc/netscapeportbut.gif" width="120" height="36" border="0" alt="Netscape portfolio version"></a></p>
{LARGE EDIT FOR SPACE HERE}
</td>
You'll also note the coder has opted for the 'scrollbars=yes' on the Netscape version which tells the browser to use the scrollbars as appropriate. Explorer interprets the iframe tag and automatically adds the scrollbars when the content overflows the frame.
Additionally, you can use layers to accomplish the same effect, to a degree. In DW, select the layer and on the overflow drop menu, select "scroll".
Hope this helps!;-)
Bozric