Hi, my computer isn't running as fast as I want. I imagine this is a
common problem. Yet I'd like to see on some kind of screen what the
limiting factor of performance is and I can't seem to find one. I
looked at my task manager (I'm using WinXP) and see a high CPU usage %
but not 100%. I see that the "Commit Charge is 555M / 1480M).,
whatever that means. And looking at the PF usage history isn't very
illustrative as well. It's just a flat line.

I'd like some kind of open-source, freeware program that will tell me
exactly which piece of my computer is underperforming right now. I
want it to be able answer questions like:

Is it my RAM? My CPU? My Video Card? Is my disk drive too slow at
7200RPM? Or does it just need to be defragged?

For reference my setup is
Athlon XP 2000+
512MB RAM DDR 266
7200RPM 120GB HD
ATI Radeon 9000 64MB RAM

And the program I am having the most performance issues with is World
of Warcraft, a video game. I am not asking for specific upgrade
advice, just a program or diagnostic tool that will help me make the
decision.

There is a program called cpu-z that will give you information about
your computer.  The website will explian more about the program.

http://www.cpuid.org/cpuz.php

~~~~

Another good idea would be to get rid of the spyware on your computer.
 Adaware is a good program for this.  This will free up resources
being used by the spyware programs.

http://www.lavasoftusa.com/

I don't believe there exists a program that will effectively give you
such information. There are various benchmarking programs (3DMark,
SiSoft Sandra, etc.) however, that can show you relative performance
of each component individually, which you can then compare to some
reference and establish which upgrade will push you closer to that
reference.

Now, in my opinion, if you want smoother gameplay in World of
Warcraft, I'd say most likely the video card is holding you back. I
know you didn't want specific upgrade advice, but even so, here it is.
The Radeon 9000 is generally a weak card for modern games, and I'd say
a $200 investment in a new video card would serve you well. If you
want to research some new cards, I'd recommend www.anandtech.com as a
starting point (the forums there are also a good resource for getting
technical questions answered).

By the way, rarely will a hard drive hold you back in gaming
performance. Typically, games are loaded from the hard drive, then run
in memory (RAM). Hence, memory size and speed is more likely to affect
gaming performance (such as frames per second), while hard drive speed
will only affect loading times, which aren't usually much of an issue.