sounds like you are getting a valid pre reg ip... my first inclination would be to look at browser issues-> reset everything in tools-> internet options to the defaults and try again. If it is windows XP, it is possible that it is having issues getting to secure sites- has the pc been connected to the internet before?
You mentioned firewall software- which one are you using/ were you using? Have you disabled it through the program itself? or in msconfig? (bear in mind that most are set to run at startup, so if you reboot it will come back on).