Help with pausing script while user logs on to LAN


I am a newbie trying to write a script that will execute an Automator application every Tuesday morning at 9am, to backup files from someone’s HD to our LAN. I would like some help writing the script so it can:
-detect if the user is logged on, and if they are not
-show a display dialog to tell the user to please log on to the LAN
-have the script wait while they do that, and then continue on with the script once they are on the LAN

Here is what I have so far:

property backupDay : Tuesday 
on idle
	if ((current date)'s weekday) = backupDay and ((current date)'s time = 50400) then
		tell application "Finder"
			launch application "Notes_03_28_08"
		end tell
	end if
	return 1 
end idle

Thanks for your help!