In the name of all that is good and holy, please remove that blinking "Under Construction" graphic. First of all, all web sites, being dynamic, are always "under construction." And if it's really under construction, it belongs on a production server or subdirectory. Just my two.
I find the black background and white text difficult to read. The red, blue and green in Enquete also clash with the black; the colors are too bright against the black background.
Why don't you try making your content area white instead. You have enough black with the background and the nav bar in the middle. I think it would just be more legible if you did that.
I'm not sure what you're asking regarding the header graphic, but the site doesn't break in IE6 or Opera 9 (I'm not home where I can check on FF or IE7, sorry).