http://developer.appcelerator.com/question/117646/help-with-splitview-and-navigation-group#your-answer

app.js

SplitViewNav = {};

// WINDOWS
SplitViewNav.masterWindow = Ti.UI.createWindow({title:'Navigation',backgroundColor:'#898989'});
/* SplitViewNav.masterWindow.add(navGroup); */
SplitViewNav.detailWindow = Ti.UI.createWindow({title:'Welcome to Burnham Parts',backgroundColor:'#fff'});


// MASTER NAV GROUP
SplitViewNav.masterNav = Ti.UI.iPhone.createNavigationGroup({
	window:SplitViewNav.masterWindow
});

// DETAIL NAV GROUP
SplitViewNav.detailNav = Ti.UI.iPhone.createNavigationGroup({
	window:SplitViewNav.detailWindow
});

// SPLIT VIEW
SplitViewNav.splitView = Titanium.UI.iPad.createSplitWindow({
	masterView:SplitViewNav.masterNav,
	detailView:SplitViewNav.detailNav,
});

// DETAIL VIEW WEBVIEW
var webView = Ti.UI.createWebView({url:"index.html"});
SplitViewNav.detailWindow.add(webView);





// CATEGORY BUTTON
SplitViewNav.masterButton = Ti.UI.createButton({
	title:'Category',
	height:50,
	width:300,
	top:40
});
SplitViewNav.masterButton.addEventListener('click', function()
{
	var w = Ti.UI.createWindow({url:'category-list.js',title:'Category',backgroundColor:'#898989',
        layout : 'vertical',
		_parent: Titanium.UI.currentWindow,
		_navGroup : SplitViewNav.masterNav,
		_rootWindow : SplitViewNav.masterWindow
		});
	SplitViewNav.masterNav.open(w,{animated:true});
});
SplitViewNav.masterWindow.add(SplitViewNav.masterButton);

var navGroup = Ti.UI.iPhone.createNavigationGroup( {
    window : SplitViewNav.masterWindow
});





// MODEL BUTTON
SplitViewNav.masterButton = Ti.UI.createButton({
	title:'Model',
	height:50,
	width:300,
	top:110
});
SplitViewNav.masterButton.addEventListener('click', function()
{
	var w = Ti.UI.createWindow({url:'model-list.js',title:'Model',backgroundColor:'#898989'});
	var l = Ti.UI.createLabel({
		title : 'category',
        layout : 'vertical'
		});
	SplitViewNav.masterNav.open(w,{animated:true});
});
SplitViewNav.masterWindow.add(SplitViewNav.masterButton);


// SEARCH BUTTON
SplitViewNav.masterButton = Ti.UI.createButton({
	title:'Search',
	height:50,
	width:300,
	top:180
});
SplitViewNav.masterButton.addEventListener('click', function()
{
	var w = Ti.UI.createWindow({url:'search.js',title:'Search',backgroundColor:'#898989'});
	var l = Ti.UI.createLabel({
		title : 'category',
        layout : 'vertical'
		});
	SplitViewNav.detailNav.open(w,{animated:true});
});
SplitViewNav.masterWindow.add(SplitViewNav.masterButton);


// WARRANTY BUTTON
SplitViewNav.masterButton = Ti.UI.createButton({
	title:'Manufacturers Warranty',
	height:50,
	width:300,
	top:250
});
SplitViewNav.masterButton.addEventListener('click', function()
{
	var w = Ti.UI.createWindow({url:'warranty.js',title:'Search',backgroundColor:'#898989'});
	var l = Ti.UI.createLabel({
		title : 'category',
        layout : 'vertical'
		});
	SplitViewNav.detailNav.open(w,{animated:true});
});
SplitViewNav.masterWindow.add(SplitViewNav.masterButton);


// HEATING HELPER BUTTON
SplitViewNav.masterButton = Ti.UI.createButton({
	title:'The Heating Helper Booklet',
	height:50,
	width:300,
	top:320
});
SplitViewNav.masterButton.addEventListener('click', function()
{
	var w = Ti.UI.createWindow({url:'heatinghelper.js',title:'Search',backgroundColor:'#898989'});
	var l = Ti.UI.createLabel({
		title : 'category',
        layout : 'vertical'
		});
	SplitViewNav.detailNav.open(w,{animated:true});
});
SplitViewNav.masterWindow.add(SplitViewNav.masterButton);


// CONTACT US BUTTON
SplitViewNav.masterButton = Ti.UI.createButton({
	title:'Contact Us',
	height:50,
	width:300,
	top:390
});
SplitViewNav.masterButton.addEventListener('click', function()
{
	var w = Ti.UI.createWindow({url:'contactus.js',title:'Search',backgroundColor:'#898989'});
	var l = Ti.UI.createLabel({
		title : 'category',
        layout : 'vertical',
		rootWindow : SplitViewNav.masterWindow
		});
	SplitViewNav.detailNav.open(w,{animated:true});
	navGroup.open(detailWindow);
});
SplitViewNav.masterWindow.add(SplitViewNav.masterButton);





// ORIENTATION NAVIGATION BUTTON
SplitViewNav.open = function()
{
	Ti.API.info('in open for split view nav')
	SplitViewNav.splitView.open();	
};

SplitViewNav.splitView.addEventListener('visible', function(e) {
	Ti.API.log('View: '+e.view);
	if (e.view == 'detail') {
		e.button.title = "Navigation";
		SplitViewNav.detailWindow.leftNavButton = e.button;
		Ti.API.log('Set button');
	}
	else if (e.view == 'master') {
		SplitViewNav.detailWindow.leftNavButton = null;
		Ti.API.log('Removed button');
	}
});


SplitViewNav.splitView.open();

category-list.js

catWindow = Ti.UI.createWindow({title:'Category',backgroundColor:'#fff'});


var catWindow = Titanium.UI.currentWindow




// CATEGORY BUTTON
catWindow.gasBtn = Ti.UI.createButton({
	title:'Gas Boilers',
	height:50,
	width:300,
	top:40
});
catWindow.gasBtn.addEventListener('click', function()
{
	var w = Ti.UI.createWindow({title:'Category',backgroundColor:'#898989',
		title : 'category - gas-boilers',
        layout : 'vertical',
		//url: 'gas-boilers.js',
		_parent: Titanium.UI.currentWindow,
		_navGroup : catWindow._navGroup,
		rootWindow : catWindow
		});
	catWindow._navGroup.open(w,{animated:true});
});
catWindow.add(catWindow.gasBtn);

var navGroup = Ti.UI.iPhone.createNavigationGroup( {
    window : catWindow
});

This crashes when viewing in the simulator.