rocknbil - 5:12 pm on Jan 23, 2012 (gmt 0)
In other words, the DOCTYPE line of code is screwing with the appearance of the page.
It will, but it is a good thing. If you validated it (sounds like you did) your site is now rendering in Standards Compliance Mode as opposed to Quirks mode. This gives you a baseline from which to debug the problem. It is also the best path to cross browser compatibility, so stick with it.
With this in place, you can say that it's definitely something in your CSS or how you've approached the layout. The fact that it's the same in all browsers actually verifies this - all of them are telling you you have a problem. Bad to leave it out? Most of the time, yes, this causes some pretty serious cross browser differences.
I've never been a fan of global zero outs (prefer to work with document's natural flow), and that may not even be it. A margin of an element within the table might be pushing things around. Next thing you should do is download/install the FireFox Firebug extension. Get on the page, right click and select "inspect element." As you mouse around the page and HTML inspector, paddings will show in purple, margins yellow, element itself blue. This should reveal what's adding the space.