Can I view websites on an iPad in an iPhone sized window?
Nope, you can't do that. But if you have a Mac, you can install Xcode from the Mac App Store for free.

It comes with an app called iOS Simulator which will let you run Mobile Safari on your Mac, including the resolution of older iPhones/iPods (non-retina display), new retina display iPhones, and the iPad's resolution.

It also implements all the touch screen Javascript events (eg: onmouseover is triggered when you tap instead of onclick, then onclick is triggered when you tap again), double tap to zoom into a DOM element, and will properly show you how things like fixed position CSS elements will appear, which is very different on Mobile Safari compared to regular desktop Safari, and it gives you all the iOS form elements (&lt;select multiple&gt; fields are completely different for example).

I'm not aware of any way to properly test your website on Windows or Linux, changing the browser window size is not good enough.