It sounds like you have a problem with spyware and maybe you are not using a
firewall to protect your network. For Windows 2000 you should be using an
interest router device such as those from D-Link/Netgear/Linksys/etc if you
have cable or DSL connection. If not use a personal firewall like the free
for personal use Zone Alarm. The link below from Microsoft explains what
spyware is and how to deal with it. AdAware SE is a great free for personal
use spyware program.