Since this topic has been dug up again, here's my input:
Create a frames page (yes I know frames are outdated) with a small frame on the top and a large frame (the page you want to search) on the bottom.
In the top page, try something like this:
function findWord(stf) //called like this: findWord("example string to find");
var sts = top.frames.document.body.createTextRange();
alert("String not in document");