styles in internet explorer

I was recently watching some of the php videos that cover using php with mysql since I already completed the other php courses and finished all previous badges for the shirts4mike website. However, I wanted to see, after the changes made to the model code that queries the products from the database, if the site would work the same in internet explorer and it doesn't :(. All the links and functionality work the same, but the styles are all messed up. I even try re-downloading Randy's css file for the site and it didn't make any difference. The colors and borders and such are still there, but the alignments and placing of elements on the pages are all messed up. I'm assuming this is because Randy used CSS3, which I know from experience IE9 does not fully support. Or is there something else I am missing?