Dreamweaver view magnification problem

Hi - hope someone can help with this. It's a strange one!

I've taken over a website created by someone else in Easy Site Wizard and hosted by British Telecom. The ESW online editing works fine and displays normally, but I get a strange design view effect when I use Dreamweaver CS3 to edit via ftp.

Using page magnification of 100%, the design view is reduced and all low resolution, looking as though it's a small version of the 200% setting.

Other sites I've created myself with an earlier version of DW just look and edit normally, not exhibiting this effect. This site also looked normal using my earlier version of DW.

Thanks

Tony