All you need to do is clear your cache and cookies !
I thought he said he'd tried deleting the browser stuff, but re-reading, he was trying to get his missus to do it so perhaps not.
As for the MAC address, if it's a cable connection, changing it is the only quick and easy way of encouraging the ISP's DHCP server to give you a different IP address. Not sure how it works with ADSL, I've only ever has static IPs on those
