I also have this very same problem on a 512kb/s ASDL connection, after the five min freeze, everything is fine (including internet and email) unless I disconnect and re-connect.
The symptoms that I have are this...
If I start Outlook Express 6 for example, the dial-up box comes up for broadband, connects to remote computer, verifies username and password, dial-up box closes as normal, receiving mail icon appears in lower right of outlook screen, clock in taskbar freezes, no connection icon appears in the task bar until the freeze clears after about five mins, upon which, the clock jumps forward to the correct time, the connect icon appears in the taskbar and my emails appear in Outlook.
Very similar pattern if I just connect to the web with IE6 too.
I use Norton Internet Security 2005, Norton Systemworks Premier 2005, XP Home, Windows update (and all other updates) are up to date. I have recently tried Microsofts Beta version of it's own spyware tool and also spybot and these have not helped me to locate the problem.
I have tried to lauch Task manager, but this is also affected by the freeze so no useful information has yet been captured.
Does this help to track down the problem? Been going on for a few months now and I can't get to the bottom of it.
My machine is older and is otherwise very stable and reliable, Abit K7 mobo, Athlon Xp2000+ processor, 512Mb RAM, 2x 120Gb IDE HD & 2x IDE DVDRW, running Win XP home. My ISP is Virgin (licenced through NTL I recently learnt) and I use a Thompson ADSL modem provided by them.