Everyone other than Sticky green is wrong. Mini-DP and Mini-DVI (at least on Mac's, who knows there may be a only digital version somewhere out there) is D+A (Digital and Analog). Just like MOST versions of DVI is actually DVI-I (again Digital + Analog).
Mini-DP/DVI to VGA is available all over, and they work just fine. And there is no DAC built in them (back to Mini-Displayport carrying a Digital and Analog signal).
OP to try and answer your question. When you say "RGB" are you referring to a component cable? This is how I understand what you are trying to to. Mini-DVI > Mini-DVI to VGA adapter > VGA to Component cable. Where your problem lies is that last cable.
VGA/15-Pin sync is separate, even though there is 15 pins, only 10 of them are used, and only 5 carry a signal. RGBHV (H & V being horizontal and vertical sync), each one has a ground as well (hence the 10 pins).
Component, even though being the same signal, carries sync over the green channel. So unless you have a way to tell either the Mac (I am not aware of any) or your TV to convert the sync, you will see a image but the colors will be skewed. You more than likely need a VGA to Component convertor that will take care of the Sync change.
Another issue you may run into (very common among older TV's), is what resolutions will your TV accept over component?
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i tried the same thing a while ago before i actually knew what i was doing.
digital to analog= bad idea. the picture will not show up well. what you need is this
http://cgi.ebay.com/PC-VGA-TV-HDTV-...622?pt=LH_DefaultDomain_0&hash=item519036ecb6
i bought this and it worked. but im warning you its very blurry and a waste of money. if your tv has no digital inputs its not going to look good.
EDIT: Prodo123, i tried that and composite and nothing worked. i spent weeks trying to figure it out calling apple once. I ended up finding the converter box. its powered with AC so it and change the signal. it shows up but... if you turn your computer to the lowest resolution thats how it looks.
Come on man, don't recommend someone buy something when you yourself really don't know what you are talking about.
Analog to Digital is fine, as long as you have a good convertor. And your convertor is not a digital to analog convertor. It is a SCAN CONVERTOR. In other words it will take a computer signal (according to the one you linked, it is VGA, which is analog), and scan it down to a SD input (composite, and S-Video which are pretty much the same).
That is why your image looked bad. It has nothing to do with Analog to digital or digital to analog.