I'm running it on a 400MHz machine with 320MB ram and a cable internet conection with no significant slowdown. I only track about 20 stocks though and when I have QT running I usually listen to music and surf the web. I also have norton antivirus, zone labs security suite and aol instant messenger running in the background. Even at home on my parents dial-up, I don't have a problem. Only the historical backfill takes a little longer. My initial reaction to the OP was, "hmm...maybe spyware?"