Ack!!!! No window cleaner!
A cloth that has been dampened with warm water is enough. No need to use a cleanser that might be abrasive on the screen. Remember that some CRTs have a thin film to prevent glare. If a cleanser that's harsh enough is used, you'll notice right away when it's wiped off (I've seen some screens with the "tracks" of where it was wiped when a cleanser was used).
Also be sure to go up and down, then side to side when cleaning.