This JavaScript Code will cycle through all elements on a page and find the next one that should recieve the focus.  This worked well in IE6 but the results in FireFox where mixed.  I don't have time right now to clean it up but I wanted to post it as this is one of those gems that you know you will want in the future.

Original Source: http://www.codecomments.com/message290822.html

Original Author: Daniel Kirsch

// returns the next focusable object for a given one
function getNextFocusElement(elm,restart,dir,_looped) {
var allElm = document.getElementsByTagName('*');
var found = false; //(start == true);
var allowedElements = 'input,textarea,a,button';
if (!dir) dir = 1;
var start = dir > 0 ? 0 : allElm.length-1;
var end = dir > 0 ? allElm.length : -1;
jslog.info('start: ' + start + ' end: ' + end);

for (var i=start; i!=end; i+=dir) {
if (!found) {
if (allElm[i] == elm) {
if (_looped) return null;
found = true;
jslog.info('i: ' + i );
continue;
}
}
if (found || (restart && _looped)) {
if (allElm[i].focus && allElm[i] != elm) {
if (isInList(allElm[i].nodeName.toLowerCase(),allowedElements)
&& isVisible(allElm[i]))
jslog.info('i: ' + i);
return allElm[i];
}
}
}
jslog.info('starting next loop...');
return (_looped) ? null : getNextFocusElement(elm,true,dir,true);

}

function isVisible(elm) {
if (elm.style.visibility == 'hidden' || elm.style.display == 'none')
return false
else
return elm.parentNode && elm.parentNode.style ?
isVisible(elm.parentNode) : true;

}

function isInList(aItem,aList,aSep,aCaseSensitive) {
if (typeof aItem == 'undefined' || typeof aList == 'undefined')
return false;

// make sure, the element is a string.
aItem = String(aItem);
if (aCaseSensitive !== true && typeof aItem == 'string') {
if (typeof aList == 'string')
aList = aList.toLowerCase();
aItem = aItem.toLowerCase();
}
if (!aSep) aSep = ',';
var lString = aSep+aList+aSep;
return (lString.indexOf(aSep+aItem+aSep) > -1);

}