Positioning text layers in the center

I'm working with a web page formed with a sliced Photoshop file. I want to add
a text field over the Photoshop image (which serves as a background for the
text). The image is about 800x700 pixels and it is positioned to always be in
the center of the browser. Using Dreamweaver to position a text layer over the
image, I can see it being positioned over the image in design view, and it
looks like it is exactly where I want it. However, when I view the page in a
browser (FF or IE) the html coding for the layer position it relative to the
left hand side of the browser window so it does not appear over the image where
it should be. I can't find or figure out how to change the html code or tags
for the layer to make it position the text over the image -- that is centered
(or relative to the center) of the browser page like the image is. There seems
to be nothing in Dreamweaver to do this. Nothing in the properties panel for
the layer that deals with positioning, other than simple x, y position (which
always seems to be relative to the left of the page). Does anyone have any
idea how I can solve this problem, that is, I think, how I can make the
positioning of a text layer relative to the center of the browser page?