This problem occurred at NYGC, noticed by a few staffs. It only happens on Internet Explorer, and for only certain sites (google.com, yahoo.com, etc.). Works fine on Firefox and Chrome. The usual approach is to clear the browser cache, reset this browser settings, etc.
I then noticed that this only happens to SSL/secured webpages, i.e. HTTPS sites.
I thought it had to do with router, I was wrong this time. The next day (this morning) I noticed that some stations (they are basically all Windows XP) on the same network works and the difference: these are SP3; while the former ones were on SP2.
Solution: Just upgrade XP SP2 to XP SP3. Problem solved.
Since it occurred around yesterday, something must have happened to the SSL recently causing this (some kind of SSL update?)
Optional note of interest: By using EventViewer->System->see "NtServicePack", and the 2 "update.exe" processes (main ~40mb, secondary ~11mb) in Task Manager, one can track the installation in real time (especially during the last phase: finishing installation-performing cleanup). I learned it from this site, When Soraima's PC is going very slow (possibly due to bad HDD, which I intend to replace).