Hello Simon,
This is the information I found searching my own archives:
activate the debug menu and choose the Internet explorer 6 windows xp
useragent in the useragent submenu.
to activate type the folowing in terminal
defaults write com.apple.Safari IncludeDebugMenu -boolean true
This is case sensitive, so to save yourself trouble, clipboard the
command as you see it here, and paste it into Terminal. I just tried
it myself and it works. The Debug menu appears to the right of Help in
the Safari menus.
If you're still having trouble, Skype me.
Cheers,
Anne