It needs a bit of tweaking in IE6. The menu and the search form seem to be all squashed up. From a design point of view, aside from what’s already been said, it could do with a little more of a gap between the menu and the rest of the page, just to break it up a bit, make it less cluttered.
I’ll offer the best feedback I can, but keep in mind I’m a design guy more than a code guy so any coding issues I would leave to the pros.
Your boxes are the Web2.0 style glossy boxes, they look sharp though I agree the layout looks like it’s a little sparse or maybe it has too much white space.
With that said the glossy boxes don’t mix well with the flat plastic look of the buttons. Worse yet the hover color on the buttons really take away from the design.
The logos are good, the color matches well (other than the tabbed buttons as stated earlier) and even though I hate it (and I know it’s inevitable) the adverts at the bottom and side don’t stand out as well as advertisements should. In my designs I try to make sure that the viewer can easily tell that something is an advertisement by either supplying that section with a darker gray background even if the ad doesn’t take up the whole space or making sure that under each ad it says "Advertisement"… sometimes both.
Take my feedback with a grain of salt, I have nothing more than personal experiences with graphic and web designs.