I think this is what you want:
window.frames['iframe01'].document.body.innerHTML
EDIT:
I have it on good authority that this won’t work in Chrome and Firefox although it works perfectly in IE, which is where I tested it. In retrospect, that was a big mistake
This will work:
window.frames[0].document.body.innerHTML
I understand that this isn’t exactly what was asked but don’t want to delete the answer because I think it has a place.
I like @ravz’s jquery answer below.