I have two IBM ThinkPad 600x's, both with W2K Pro SP4, Office 2000, ZoneAlarm and AVG 6. One of them (with 132 MB RAM, the apps include Office and learning games of Knowledge Adventure) has become very slow, booting up takes over ten minutes and everything else is also very, very slow. (The other, with only 64 MB RAM works OK) In safe mode (with networking) the PC appears to work at normal speed. I Have ran defrag and approx 60% of the HDD is free. Ad-Aware did not indicate any problems either.
After reading whatever I could find on the topic, I decided to reinstall the OS. First, the setup found a damaged OS and suggested to repair it. The setup took overnight to complete, but did not solve the problem. Then, I started the PC in Safe Mode and launched a clean installation. The setup started much faster, but turned sluggish at the "Installing Devices" phase when the blue completion indicator bar was at approx. 60% For example, after clicking the "Customize" button of the regional settings it took several minutes for the "Regional Options" screen to show up.