Bladerunner - I think you and TerraMex have the idea wrong, I suspect through a misunderstanding of exactly what your chart means.... I think that if you built the system the way you describe, it won't do very much, and might very well make your condensation problem WORSE!
Your chart describes the dew point, or what temperature condesation will occur at if the air is FULLY SATURATED with moisture. Or, in other words, given air at a particular temperature and relative humidity, how much it has to be chilled in order to have it reach full saturation and start condensing.
The term "Relative Humidity" describes the RATIO between the amount of water that a volume of air at the given temperature could theoretically hold, versus the amount that it is actually holding. (note that pressure also effects this, but not as much so, and can be ignored for our purposes) At least at the temperatures we are talking about (~10-60*C) cold air can hold less water vapour than hot air.
Thus if you take a given volume of air, and evaporate a specific amount of water into it, when you heat the air, it's relative humidty will DROP, and so will the dewpoint. If you cool the air, then it's relative humidity goes UP, along with it's dewpoint.
The most visible common example of this is a summertime thunderstorm - Air close to the ground is heated and becomes saturated with water, then rises as a 'thermal'. As it goes up, it cools, becomes super-saturated, and condenses, making a cloud. When the weight of the water in the cloud becomes more than the rising air can support, it falls as rain. The falling rain cools the thermal, shutting off it's flow, and the now unsupported water falls abruptly. (This is a gross over simplification of the process)
As another example, if you go into a dry heat type sauna (NOT a steam bath) with a cold can of Buttwiper (I wouldn't insult Guinness by cooling it that much!) you would not get much (if any) condensation on it, because the relative humidity is so low that the dewpoint is lower than the temperature of the beer can. (Once the experiment is completed you can cook some hot dogs with the lousy beer, and get a nice dark beer out of the properly non-functioning Lucas Electric beer cooler
)
Now as it applies to your design proposal, what you seem to be trying to do as I understand it, is cool the air entering the case, without changing the amount of water vapour that it's carrying other than possibly having some condensation on the incoming air radiator (which really won't help much).
To pull some numbers off your chart, picking a fairly bad case scenario....
Assumptions - per your previous posts, and my guestimates....
1. Your rad is at 13*C and your blocks are at 12*C
2. Air going through the rad will be cooled 5*C from ambient.
Assume 30*C and 75% humidity (which the person from Southern Louisiana would consider wonderfully comfy...) The dewpoint is 25.1*C. Condensation would occur on your blocks at 12*C.
Run the air through the rad. it is now at 25*, and the dewpoint has now dropped to 20.3*, and condensation is still occurring on the blocks. Even with a really big drop to 20*, your dew point is at 15.4* and condensation is still happening.
But wait! you say, wouldn't there also be condensation on the rad? Yes, there would be, but the amount of water removed would only be enough to leave the air exiting the rad near saturation for the lower temperature. The dewpoint of air at 25*C and 95% humidity is 24.1*C, or ONE degree less than the result with no rad at all.... :shrug:
If I were trying to design something to deal with this, I would probably try to make a box with little or no airflow and try to dehumidify that air some how. Possibly you might also be able to do the same rad and chimney setup, only locating the CPU box ABOVE the chimney.
This way you make a sort of 'fanless dehumidifier' where the air would enter the rad, be cooled so as to get lots of condensation, and then reheated to ambient (or a bit higher) which effectively lowers it's relative humidity. If you can drop the humidity to 30% at 30*C by doing this, your dewpoint in the PC case becomes 10.5*C, and you'll have no condensation.
(I would note though, that those numbers would leave less margin than I would feel really comfortable with...)