Geek failure. In following various suggestions I seem to have added "WinXPDisableZeroConfiguration.exe", which I'm pretty sure is the disable program from here, and now *it's* eating my processing power. It's a registry modification and I not only don't know how to delete it, I'm afraid to try because, well, registry stuff. Augh. Unlike the earlier problem, using the task manager to shut it down does bring my CPU load back down to normal.
However, Flash still seems to be crashing the browser/computer, so at least *that* hasn't improved.
ETA: OMG. marith is totally a hero of the revolution. She has told me about MSCONFIG and sysinfo.org and I have at least gotten the WinXPDisable thing turned off and am going through the task manager to figure out what unnecessary shit is running on my computer and TURNING IT OFF. All hail Marith! Huzzah! Huzzah! Huzzah!