What you need to do is get the html validator plugin for firefox, which will show you all your mistakes when you view source.
If you're doing this yourself, then you're doing fine - it's a learning curve, and boy! does it eat into your time.
But it's the only way if you want it to look exactly how you want it (unless you're very rich, in which case it's not the only way - but you then have to spend a lot of time finding someone reliable who's going to be around long-term etc.)
The usual reason for not showing up in nasty old IE is the wrong doctype - put a strict doctype declaration at the top of the page, and then you can't go wrong provided you then go through the page removing all errors. You only need one error for it to cascade down, as mentioned above.
Strict xhtml usually simply has /> added at the end of it and isn't in any way difficult e.g
<img src="blah.jpg" />
<div> another blah </div>
<h1> more blah </h1>
For example, one missing end div e.g no </div> will usually destroy the whole page as the browser tries to figure out what the heck is going on.
Buy html, xhrml and css by Elizabeth Castro, which is the most useful book I've ever found on html. I use it all the time and I've been learning this stuff for years.