I'm not sure about the preferences, but it's a good idea to have your color settings match in both programs. In CS3, under the "edit" menu, select "color settings" and choose the color spaces which are appropriate for you. I have custom settings (which you can save and name) for photo work, offset print cmyk, and rgb web work. I prefer the ProPhoto space to work in. So that's the setting I use in the Photo custom setting. You can then set Lightroom to use that for its exports as well.
On the LR side, I remember there's a way to select the program you wish to use for editing out of lightroom. Once you pick PS CS3 and the export color space, just select the Command and "E" keys and it will start the process to export a copy of the file you're working on to PS. When you hit save while editing it in PS, it saves the .tif back to your lightroom library alongside the original.
Sorry if this is a bit long winded, I just woke up from a nap and I'm kind of foggy.