IE and firefox compatability problem

Hi, I am new to this forum so I'm not sure if this is in the right place, but i am designing a e-commerce website for a local company, and have come across a rather annoying problem!

The problem i have is that my site design will show correct in mozilla firefox, but when I view it in internet explorer 8, it seems to centre everything on my page. I have tried chanigng all my CSS into an external file but to no use. In firefox, my site is aligned to the left but IE seems to ignore this... I am quite new with CSS, so any help would be appreciated.

Thank you,