tell application id "com.omnigroup.OmniPlan"
	set oDoc to front document
	set lstFredTasks to my PersonTasks(oDoc, "Fred")
end tell

on PersonTasks(oDoc, strName)
	using terms from application "OmniPlan"
		tell oDoc
			set lstRes to (resources where (resource type is person) and (name is strName))
			if length of lstRes > 0 then
				task of every assignment of first item of lstRes
			else
				{}
			end if
		end tell
	end using terms from
end PersonTasks