Rather than putting your content into your sliced table, use DreamWeaver's layer tool to add a layer on top of your sliced table. Put your content in there. You'll be able to expand that like you want, or make it scrolling. This would be the absolute simplest thing to do.
If you want a design that expands to fit the content, that's a lot trickier and ImageReady doesn't support that. You might want to google some stuff up on Liquid Layouts, but ultimately liquid layouts tend to use more whitespace between the items - very different from the route your design is going down now.
Lastly, and forgive me if this is off-topic, but you might want to abandon slicing altogether. The HTML is brittle, old, and heavy. I helped write a Photoshop plug-in called SiteGrinder. It's a much more natural way of moving between Photoshop and DreamWeaver, and you don't have to slice. It'll let you leverage your Photoshop organization in DreamWeaver rather than fighting it.
http://www.medialab.com/sitegrinder Anyway, enough said. Check it out.
Hope this helps,
Chris Perkins
Media Lab, Inc.