Depending on the type of files you were downloading, it might be your anti-virus or anti-spyware or whatever that is causing high CPU usage. I know that when I had Norton antivirus 2004 on my computer, it would constantly be checking the files as they were downloading, and would pretty much make my computer unusable. There are usually settings that you can check to see what kind of files are scanned automatically. Unless it is some type of executable, it probably doesn't need to be checked while it's downloading, just when you try to open it.
But that might not have anything to do with your particular case. It could be another program that is interfering, or it could be BitTornado itself, or it could be your operating system... I don't have much experience with windows ME since I found it to be a nightmare to keep running stable. It seemed like any little change I made could potentially get it to blue screen
Or, it could be hardware related... there are so many things that could be causing it, and the only way to find out is process of elimination.