Norton.... yuk.

Check services. Check running processes.

Run hijackthis! and cull all the garbage out that may be eating up all the bandwidth and system resources.

Clean it all out by uninstalling everything not required and start again. Most likely this will work a treat, providing you don't wreck the system getting rid of Norton.

This is my HijackThis! log. Note it's extreme brevity.
My system is fully functional with everything expected of a PC including file transfer, banking, comms and server operations, yet as you can see, my running processes are trimmed down to the bare minimum without all the security garbage that bogs everyone down. My kickass firewall is the kingpin of my security regime, I haven't had a problem since it's installation after I got the dreaded Blaster Worm years ago.

Logfile of HijackThis v1.99.1
Scan saved at 9:24:22 PM, on 25/09/2006
Platform: Windows XP SP2 (WinNT 5.01.2600)
MSIE: Internet Explorer v6.00 SP2 (6.00.2900.2180)

Running processes:
C:\WINDOWS\System32\smss.exe
C:\WINDOWS\system32\winlogon.exe
C:\WINDOWS\system32\services.exe
C:\WINDOWS\system32\lsass.exe
C:\WINDOWS\system32\svchost.exe
C:\WINDOWS\system32\svchost.exe
C:\WINDOWS\system32\ZoneLabs\vsmon.exe
C:\WINDOWS\Explorer.EXE
C:\Program Files\Zone Labs\ZoneAlarm\zlclient.exe
C:\000_SAFE\000_Program Bin\Hijack This\HijackThis_1.99.1.exe



O4 - HKLM\..\Run: [Zone Labs Client] "C:\Program Files\Zone Labs\ZoneAlarm\zlclient.exe"

O17 - HKLM\System\CCS\Services\Tcpip\..\{xxxxxxxxxxxx}: NameServer = (my ip's here)

O23 - Service: TrueVector Internet Monitor (vsmon) - Zone Labs, LLC - C:\WINDOWS\system32\ZoneLabs\vsmon.exe



I'd bet good money that the PC in question has pages of content in a HiJackThis! scan log with a possibility of a few conflicting security programs running.