the air con into case thing works well, so long as you seal it up so that the only air going into the case is from AC and make sure there is a good airflow path provided by outlets to cool everything. however, you can get the inside of case cold to the point that condensation forms on the outside of the case, if this drips inside the psu, all bets are off.
if you blow through a rad, you can massively drop the resultant water temp (given a longish runtime) by ducting the air out of the rad back into the intake for the ac, so that airflow is AC>rad>ac>rad>ac etc.
you quicly hit the thermal cutout temp doing this however. you also want to make sure its as airtight as you can get it, then stick a bunch of silica granuals in to remove all the moisture from cycling air (else you will end up freezing the rad/evaporator into a solid block of ice)
*edit* my typing........ argh
**edit**
Putting thigns inside freezers/friges will usualy result in one of the following:
pc overheats and dies because there isnt enough heat pumping capacity to get heat out of the insulated box you jusst put it in
the compressor overheats and dies because it wasnt ment to run constantly, 5 mins on, 30 mins off would be a harsh life even! (afetr this fails, the pc follows very soon after)
the refrigerant escapes due to failing seals due to them not being designed for constant load, this kills compressor then the pc.