Bedevilling problem:
The menu and submenus, called from within iframeA worked wonderfully well manipulating the content of adjacent iframeB until any submenu had so many menuitems that scrolling kicked in and zooks! it reformatted the page to where iframeB disappeared from view as the page reformatted causing iframeB to go below iframeA and of course a vertical window scrollbar appeared to accommodate the reformat [window scrollbar not to be confused with the submenu's scrollbar - both appear simultaneously.]
Assuming it was the sudden appearance of the menu's scrollbar, I turned off menu scrolling but the problem persisted. What appeared to be happening is that when the submenu grew to where its top equaled the top of iframeB, the browser interpreted it as an extension of iframeA and gave it spacial preference over iframeB, bumping the latter to the nether
regions. It mattered not whether one had the tag valign="top" as an iframeB parameter.And if I gave the submenu a top="x " [e.g. top="10" or even top=0 or even top=""] setting, the page would simply load with iframeB already bumped to the
netherworld, as if the browser was so 
smart as to be pre-reading the submenuitem on loading. The particular site design allows for scrollbars for iframeB and for the submenus but NOT for the page itself.I stumbled on a solution I hope will help anyone with the same problem. Add top= to the submenu [just top=, no value or quote marks]. For some reason it solved the problem.
But for the future, does overflow="scroll" have a parameter that can set the size of the scroll. That should work too. /mfurf