If you prune through this article you will probably be able to gather most of the information you seek, but I'll try and summarize the relevant bits.
First, you should understand that MSAA is a type of Supersampling anti-aliasing (SSAA). SSAA, also known as FSAA, removes "jags" from an image by rendering the image at a higher resolution:
Full-scene anti-aliasing by supersampling usually means that each full
frame is rendered at double (2x) or quadruple (4x) the display
resolution, and then down-sampled to match the display resolution. So
a 2x FSAA would render 4 supersampled pixels for each single pixel of
each frame. While rendering at larger resolutions will produce better
results, more processor power is needed which can degrade performance
and frame rate.
MSAA is a more efficient form of FSAA, but the multiplier still has the same meaning, roughly. This means (as you probably know), that a higher multiplier gives better results, but demands more processing power.
CSAA is an even more efficient form of SSAA, which uses some advanced 3D magic (just read the paper if you really must know) to deliver better results:
In summary, CSAA produces antialiased images that rival the quality of
8x or 16x MSAA, while introducing only a minimal performance hit over
standard (typically 4x) MSAA.
In essence, if you equate your multipliers, MSAA will produce better results than CSAA (though it is implied that the results will not be significantly better), but will demand significantly more on the processing power department.
QCSAA is simply CSAA with twice as many sample points used to perform the anti-aliasing, so obviously QCSAA is better than CSAA.
Wikipedia's Supersampling article actually provides a great image showing why more samples mean better accuracy:
All this being said, the order in which DiRT2 lists its anti-aliasing options looks perplexing, to say the least. Since I doubt you can personally tell the difference once the multiplier hits 8x and upwards, I'd stick to CSAA/QCSAA for the performance gain.
Finally, here is a nice comparison shot of the various techniques on a specific, simple, image (from the article in the first link):