A simple search HDMI convertor to (type you want) is easy to do, last time I posted a link about this the site took it down so you will have to search yourself. However do check your convertor will support HDCP, it is a digital copy protection and means that cables and adaptors that don't support it do not won't allow you to play that type of media, most stuff from you purchase will have HDCP built in. Usually only HDMI supports HDCP. If you have a good store nearby ask them.
You will lose quality whichever you chose but as your tv is not HD you need to check it supports Apple Tv minimum requirement as below from the apple website.
- Compatible with high-definition TVs with HDMI and capable of 1080p or 720p at 60/50Hz,2 including popular models from these manufacturers: Hitachi, JVC, LG, Mitsubishi, NEC, Panasonic, Philips, Pioneer, Samsung, Sharp, Sony, Toshiba, Vizio, Westinghouse