How about this...
You only have so much width you can fit tabs into. So first of all, decide how many tabs you can have on your screen - possibly based on the average screen/viewport dimensions, which I think these days is 1024x768. Lets say you have space for 7 tabs.
Next, choose the most important 6 site areas, and put those into the first 6 tabs. Then, anything else goes into a dropdown list in the 7th tab. It doesn't have to be a nasty looking dropdown either - there are
tricks for making dropdowns look sexy.
Finally, yes, it's a great idea to show the subsections when you hover over a tab. It's quite a common thing to see. Use some javascript and DOM manipulation to make the subsections appear when you hover over a tab. *Don't* use this technique for the 7th tab (if you're concerned about accessibility). Your 7th tab must be a dropdown, because it must work without javascript, or all the options in it will be inaccessible to a browser that has javascript disabled.