There are many products that do this. Here is an example:
http://www.ramelectronics.net/html/PC-TV_video_adapter.html
I have never used this particular product and don't endorse in any way. I
am just linking you to this site because it came up on google, and it can
show you the kind of thing you are looking for. Perhaps, someone else here
has a particular converter that they have used and can recommend.
--David
--
David M. Marcovitz
Microsoft PowerPoint MVP
Director of Graduate Programs in Educational Technology
Loyola College in Maryland
Author of _Powerful PowerPoint for Educators_
http://www.loyola.edu/education/PowerfulPowerPoint/