Network login corrupts display

A new system with a Asus CUW-E motherboard based on Intel’s 810e chipset with an integrated Intel 10/100 LAN adapter runs fine until my customer logs into his MS Small Business Server network. The display immediately becomes corrupted – the fonts become beome huge, the pop-up windows become solid grey boxes and the system is unusable. I have never run into this and am perplexed! Does anyone have any ideas?