I have had XP Pro for a number of years now, and I know full well that after a while it had always deteriorated and I would have to format. This happened for around the third time where it became nearly unbareably slow. I figured since it keeps happening, and to generally get with the times I may aswell purchase Windows 7 and do a completely fresh install.
I initially only had only 600(and something)MB of RAM so I looked at Windows 7's required specifications and went out and purchased 2x 1GB RAM.
I have an Intel Pentium 4 2.66GHz processor and from Windows recommendations this exceeded their requirements so I stuck with that.
Now, I literally installed the new OS, installed Firefox, Avast! and a couple of other programs to get me going. I then noticed that when viewing videos in Firefox that it was extremely slow, and I then added the Gadget to the desktop which tells you CPU usage and noticed that this seemed to spend more time at 100% than not! I proceeded to run Spybot S&D to see what it would pick up, while the scan was running it was near-impossible to use the computer and here are a couple of screenshots showing the usage:
After Spybot S&D completed it's search it then found 6 things, which were removed, all of the latest Windows Updates applied and restarted. It is now sitting at 100% again.
I removed the two smaller RAM sticks today, so I'm now left with the 2x 1GB in the machine now. I also put them in the correct slots for 'optimal performance'.
Here's a screenshot of playing a normal video through Firefox, which works absolutely perfectly on my laptop:
This is not merely down to the plugin, it's just whatever process is doing (what should be) a fairly simple task at the time.