Hi Chantelle.
There are a couple of things you can do.
in the DW page properties section (Ctrl-J) there is a spot to set top and left margins set those four boxes to 0 ... then check your body tag and see what changes DW made -- then you can easily hand code them at any time -- it puts the necessary tags for both Exploder and Netscrape.
The second thing is create your slices so one area is "generic" enough it can repeat/ tile
Macromedia has a quicktime video on their site which will walk you through how to make a "flexible" table which will fill your browser window.
Heres the link to the Autostretch tutorial. Hopefully it will give you some ideas
http://www.macromedia.com/devnet/tip/005.html
This is kind of hard to find on the Macromedia site, but heres a list of other usefull quicktime tutorials
http://www.macromedia.com/devnet/tip/archive.html
hth
stan...