IE6 not responding for standard users after deploying XP Service p

I have recently deployed xp sp2 to a number of machines. most machines work
ok but some have problems with internet explorer.
IE hangs & stops responding when accessing some sites but if the user is
given elevated privileges (eg being added to administrators group) the site
then works fine.

oddly www.yahoo.com works ok while www.yahoo.co.uk causes IE to stop
responding.

any help would be appreciated.

thanks