Internet Explorer wrecks havoc on my site

I’m relatively new to WordPress, and I know there are a few validation errors that I don’t know how to correct. However, I made my site with firefox as my browser and it displays perfectly. But when I open it with Internet Explorer, my top links are too high, half the header images are missing and/or not in the correct place, the images on my other pages are overlap eachother, and my footer is missing!
This is my site http://www.antsarts.com
Please help, I don’t know what to do.