AMD Athlon XP 2800 does not compare to the two pentiums. As for the P4 2.8 vs. P4 2.6 HT, it depends on the applications you're using it for. Certain things can process better with the dual threads, while other things process worse.
Those articles are for admins on networks who have people sharing machines a web server usually only has one login in anywas root. It is saying if you have a machine with admin , bob and joe that joe can login in and steal info from admin you won't have 3 logins on your dedicated server just one.