XP won't allow DHCP IP address assignment

After the last lot of auotmatic updates (about 28/02/2005
in the UK) I cannot connect to my ISP - they say it's a
known problem with XP which doesn't like cable modems. The
system cannot obtain an IP address using DHCP. I've tried
resetting the IP manually using 'netsh int ip reset ...'
but that doesn't work. I tried to uninstall the update and
get 'Tag invalid' errors so that I can't uninstall. Has
anyone else had this problem, and can anyone suggest a
solution - short of throwing the computer and/or modem away
and starting again!