Desktop PC freezes only when on Internet

  F27Rules 14:50 20 Dec 2009

My computer only freezes whilst connected to the internet (using IE or Outlook Express), disconnected from the internet it is fine. Also froze when I tried Firefox.
Saw a blue page once which said,
" problem has been detected and windows has been shut down to prevent damage to your computer !RQL_NOT_LESS_OR_EQUAL
If it is the first time re-start........ if not follow these steps check hardware/software up dates, disable BIOS memory such as caching and shadowing.
Tech info
*** STOP: 0X0000000A (0XFFFFFF94, 0X0000001C, 0X00000000, 0X80500105)
Beginning dump of physical memory,
Physical memory dump complete
contact for further assistance"
Computer Restarted okay.Phew!
So only when using internet for 5-15 minutes it freezes , and has to be restarted using the on/off switch, as the only way to carry on, cont-alt-del does nothing.
If the Ethernet lead is disconnected , PC works fine usually for hours, but does also on occasion freeze.
Reconnect ethernet lead and freezes in minutes.
So far , I have
Downloaded XP SP3, it had caused problems before, but seems okay now.
Downloaded latest driver for NVIDIA 6800GS graphics card
.Tried using Firefox rather than IE7, but problem persists
.Used malawarebytes to remove more Malware, I think brought in by Firefox.
Unticked "enable third party browser extensions" on IE
Ran IE7 without Add Ons
Disabled Google task bar
I now see that all previous system restore points have gone.
Downloaded Spybot which found some threats.
AVG ( found trojan horses Generic 16.CKT and Downloader.small 61.BW. AVG only sees the C Drive, not the F and G,
Computer is really running very slow now, I have just doenloaded Microsoft Security Essentials, in case AVG 9 has caused problems.
Even right clicking "My Computer" takes ages to see the drives, and AVG resently showed Drive F was not formatted.
I do have the original XP disc, if a re-load is required.
Have Intel Core CPU 4300 @ 1.80 GHz, 2 GB RAM, NVIDIA 6800GS graphics card, Windows XP SP3.
Computer has three drives, C-for software, F and G for mostly photo storage. Network card is part of motherboard (???Rhine??)

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