I have a VGA to RCA cable and an Intel Graphic Media Accelerator video card, but I'm not sure if my graphics card has TV-Out function capability through the VGA and if Ubuntu supports this. My laptop is Acer Aspire 5740 with Core i3.
Typically, these VGA to RCA cables fit to a specific graphics card several generations back. It worked by re-assigning specific pins on the VGA plug to put out composite signal (often called "TV-Mode" or similar in the driver software). you didn't get it with your laptop, did you? today's graphics cards can't do this anymore, and this cable won't fit your card.
If you want RCA/composite video out of your laptop, you need a so-called scan converter. Prices range from about 30€ to several hundred €, quality varies from cheap china knock-off without adjustable parameters to broadcast quality equipment.
I use a model similar to this. It's a reasonable compromise (for me) between price and quality.