|and if it's personal computers then I think the default settings of XP SP2 and other standard firewall is ignoring icmps? so it's a bit unreliable...|
so, without asking them to install a webserver, you can also check for IMs the computer use, there're some tutorials on doing this (testing if someone's Y!m, AOL, MSN, ICQ is online)...
you still need serverside scripting though
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