The closest you're going to get for what you want is using CSS positioning. You would use the following two properties:
left: ##px; - specifies the number of pixels from the left side of the page you want the element to appear.
top: ##px; - specifies the number of pixels from the top side of the page.
If you want the element positioned relatively, depending on the users's monitor resolution, then you can use percentages. As far as I know, there is no way to use a Cartesian Coordinate system in the same syntax that you want. The method I mentioned above is the same thing, it's just written differently from (X,Y).
left: / The X value /
top: / The Y value /
Then you should position everything absolutely. In CSS:
the only problem is, if you're dealing with text, Mac and Netscape users can increase text size regardless of how you specify text sizes in CSS (px, %, relative, points...). You would also need to specify the width and height of each element. Then if someone has increased the text size displayed in their browser by way of their browser settings, text may overlap the edges of the elements you made. Then in CSS:
The last property, overflow, tells the browser what it should do with content that spills over the edges of the element that contains it. In this case, it would cause the browser to display scroll bars if it should need them.
Pretty much everyone that I know who uses CSS to lay out a page, including me, recomends NOT using absolute positioning and depending on specifically sized elements. In web design, there is NO guarantee that text will be a certain size and that a viewer's screen will be a certain width. It's one of the finer miseries of what we do.
You could using pixel perfect positioning, depending on what you are doing on the site. If you are laying out text areas, avoid pixel-perfect positioning like the plague. It always gives more headaches than it cures.
Are you coding in XHTML using CSS to lay the pages out? If so, visit http://www.alistapart.com/. It has a bunch of info on CSS layouts.