Use my Laptop to play movies on an analog TV

digital TV converters take digital air TV (via an antenna) to analog (typically coax), This signal is typically SD running 480i/p at 30fps. They are not made to handle computer outputs which are typically 60fps 720p or 1080p, and generally do not have the hookups do to so either (but some high end units may do the trick).

There are some specific converters that will take HDMI input to composite output, but there may be a frame or two delay between the audio and video unless the box processes both audio and video together (like in a surround sound receiver or something).

When it comes down to purchasing a $1-200 converter or receiver vs a cheap digital TV, you can take bets on which I would jump on.

Many older TVs still had HD hookups (like component RGB), and there are some cheaper realtime converters which will go from HDMI to Component if that is an option, but to go to S-Video or Composite is a whole different ballgame.