Nope not on https server and not got ssl enabled either.

Ok decided to do a test while typing this as i had a hunch, and yep im correct.

Its a stupid Internet explorer issue.

Works fine in FF and Safari etc but IE thinks its being clever by asking if you would like to see the secure and non secure items together.

I see your problem that if people use IE and see that they are more than likely going to click yes, which when then render the page a mess again.

Hmm not sure how to get around this...will have to have a think.
Least all the text is still readable now, before it was all bunched up for me.

I think that moving the images and css to worldpay and linking to them would sort the issue out, but thats just too much hassle, especially if you change some css or images etc, then you will have to re-upload them to the worldpay site.

Have you tried doing a test transaction in a different browser, like FF or safari?