Windows Explorer Not Showing Site Correctly

Hey Warriors

I've nearly finished a sales page i have made for someone but theres a problem ... it was all going fine and i thought it was coming on ok untill i heard from my client who said

" Hi Ricky I've just opened up the sales page on my wide screen and it does not look right, the header is pused to the left and the content is streached"

Of course i didn't have a clue what he was going on about it looked fine on my PC, but i had to investigate further, after about 30 mins i tried opening it in Widows Explorer instead of Mozilla Firefox and Boom there was the problem.

But i don't have an explanation for this, at first i thought it might be due to my header being too wide so i cut it back down to 770 Pixels, but its still the same, i created the sales page using XSitePro2, and i have emailed them but have got no reply yet.

Hoping to get a quick awnser from your Guys since you haven't let me down yet

Thanks again warriors

P.S
i haven't forgot the awber box to get there email address just waiting for client to buy an account

Ricky