IE7 not resolving after SP1 install

After Vista SP1 installed a couple nights ago, browing to a website has come
to a crawl, taking 10 secs or more to load a simple page (if at all), and it
would appear that the DNS is not resolving correctly (I always see the IP
address in the lower left of Explorer -- not the resolved name).

I disabled phishing filtering and defender but that didn't resolve the
issue. Am on a simple Win2003 server SP1 domain, running DNS for a public
website, and the usual ADS, DHCP, etc. A hardware firewall acts as my
perimeter DNS router -- routing web 80 requests from the cable modem to the
server's internal address on the network. Vista firewall is disabled. This
config has been running fine for years w/o issue. My laptop, which is also
Vista but not SP1, pops fine; and the Win2003 server the same -- IE 7 on
both. Just the SP1 machine has this issue. Norton 360 AV on the 2
workstations and most of the software is the same for the Vista machines
apart from the SP1. DHCP points only to Win2003 DNS for resolution -- not
external DNS servers of my ISP. Of course the firebox has the external DNS
nameserver addresses.

Any ideas/thoughts?

Thanks in advance (I cross-posted to IE7 as well)