hi;
and your welcome (though i really didn't do anything - clearing your Temp Inet Files caches may have helped...do it regularly - see IE Options | Advanced Tab | Clear TIF...blah-blah)

-- but it's real nice to get a clear concise t-shooting checklist as a reply, and you've answered all questions i asked comprehensively too. Nice quality to have when asking for help.

All i can say about about a "TCP acknowledgement attack" is that it's likely an ICMP pinging from a site's AdServer (cookie related perhaps even)....I've only used ZoneAlarm in the past,and now i'm not using a software firewall (too resource intensive for my liking - but i don't suggest this for 'most' others - and I'm behind a Router, plus www.GRC.com ShieldsUP tests show all my PORTS are STEALTH I don't even use winXP - so YMMV

The Option to not use the Cache in the Java Plugin is likely due to it's old version then...
Look here (note the "Location" bar address) and go there in WinExplorer and look for a folder called "Cache" and clear it (manually) if you find it filled with junk;
http://java.sun.com/j2se/1.4.2/docs/...nel.html#cache
(obviously - substitute 'your' %USERNAME% where \LouisMartin\ is in the PATH)

here's another XP Java article you should see;
http://www.mvps.org/marksxp/WindowsXP/java.php

There are many articles about Java VM and just upgrading it can be a PITA, and break your system - so go slowly if you decide to and be careful Heck, if it ain't broke...don't fix it

Enjoy your stay here
I know your questions and methodical tshooting replies will help others whom read this, looking for assistance

*edit;
and since you were so sincere, and i know now you use IE regularly - this will help you configure it's 'Security'
https://netfiles.uiuc.edu/ehowes/www/btw/ie/ie-opts.htm