I agree with buntine on the sans-serif font. It would at once look more professional.
Don't go for 3D things on the banner, it will just make it a bit "I just bought frontpage and look at my website, those pipes just RULE !!!".
Being a scientist myself ( biologist ), I would suggest to keep the design simple, sharp-angled, maybe even a bit hard. ( that's my opinion for looking at scientific websites all the time, and also at the ads in the scientific magazines ).
I hate blue in website, but I think it's a good idea for a chemestry-oriented website.
Though, you shouldn't put as much blue...
Go for a smaller header. Give highest priority for to the contents.
And make it wider. Or center it in the page.
Also, the page is really long. It doesn't fit in my 1280x1024 screen resa.
One last thing, and it's directed to everybody :
What is really the point of putting this w3c buttons in the layout ??? I mean, people who come and look at your sites are not webdevelopers, they are scientists ( or whatever.. I said this applied to everybody ). They couldn't care less about seeing the site is w3c validated, most of them don't even know what that is, and if they click on the buttons, they won't understand a thing.
Ok, I see, you want everybody to know that your code validates. But I mean, isn't it normal that it validates ? It's your job, after all !!! It's like, a taxi driver who would brag about having his driving licence...
If you really need to put the buttons, you can put it somewhere else, and not use that much space for things people don't care about.
Sites offering web services can keep the buttons, but obviously, people who contact them to make web designs don't know how to do them by themselves, and don't care about a w3c validation, because for them, it's normal.
Ok, I'll stop harassing everybody with that. I just wanted to point it out once in my life.