Crashes... any diagnosis?

OK, I'm having crashes that I just can't seem to solve.
They happen ONLY when I'm using the internet, not when the connection is idle. I happens in Itunes, firefox, and IE. It happens most frequently when I'm using the most bandwidth. (Downloading big files, etc.)
I've changed network cards and reinstalled drivers, to no avail.
Sometimes, it gives me a BSOD, saying hardware failure, call your vendor. Sometimes, it just reboots, and sometimes, it just freezes.
Oh, and often, I will try to go to a webpage, and it instantly tells me, without even looking, it says the site is offline. When I know darn well it isn't.

The fact that I've used different NIC cards and had the same problem suggests to me that it is a software problem, but I can't figure out what.

Any help?

(Windows XP pro is the OS)

Open Event Viewer (in order to access the error logs, and check for any critical errors)...Start | Run | Type eventvwr.msc and click OK | Highlight "Application" and "System" independently in the LH pane | Right click any error message(s) (critical errors are in Red), and select "Properties" | Write down a couple of the latest critical error messages exactly as they appear under the "Description" field, and post them in this thread.

Also, open the System Information tool by typing msinfo32 in the Run box | Expand "Components" | Highlight "Problem Devices", and look for any problems that might be listed there.

I did that. Nothing in the problem devices.
The only issue in event viewer is this:

In applications:

Source: LoadPerf
Codes: 3011, 3012

Unloading the performance counter strings for service WmiApRpl (WmiApRpl) failed. The Error code is the first DWORD in Data section.


Also:

Source: Userenv
Code: 1524

Windows cannot unload your classes registry file - it is still in use by other applications or services. The file will be unloaded when it is no longer in use.

I tried using the solutions provided by Microsoft, but it doesn't seem to help.

What are the rest of your system specs, including PCI bus speed (you can use a program like ClockGen to read the bus)?

It's a 2.4ghz P4 C on an Abit VT7. It's running at stock speed, so my pci bus should be 33mhz. Geforce4 MX420, Samsung 1614C SATA hard drive, generic CDRW and DVDRW drives, either motorolla WPCI810G or viewsonic WPCI-100 802.11G adapters, Phillips PSC805 USB sound card, plenty of good memory, an adequate power supply, and adequate cooling.

This could be a problem...
I think you may have a corrupted Performance Counter...download the Exctrlst.exe (Extensible Performance Counter List) utility from the following MS site...

Exctrlst.exe: Extensible Performance Counter List
http://www.microsoft.com/windows2000/techinfo/reskit/tools/existing/exctrlst-o.asp

The program installs itself to "C:\Program Files\Resource Kit". Run the exctrlst.exe, and in the Extensible Counter List (ECL) window that opens, scroll down to WmiApRpl and highlight it | Uncheck the "Performance Counters Enabled" checkbox | Close out of the ECL and reboot. The following KB article may also be of some help to you...

How to Manually Rebuild Performance Counter Library Values
http://support.microsoft.com/default.aspx?scid=kb;en-us;300956 ...use this method only if unchecking the "Performance Counters Enabled" checkbox, as I noted above, doesn't help your situation.

It doesn't seem to have helped.