if file is there

I want a script that will let me do the following
If a file is at /applications
then Display dialog “”
Hope this is enough info…
Basically i want applescript to locate a file on the hard drive and if it’s there then practically display dialog “Yep it’s there”

tell application "Finder"
	set file_name to "Address Book.app"
	set x to path to applications folder as text
		set y to x & file_name as alias
		display dialog file_name & " IS in the Applications folder!"
	on error
		display dialog file_name & " is not in the Applications folder."
	end try
end tell