Apple has started to market a low-cost iMac 20" for students and schools. Sold to 899$, it has a 2 GHz processor, a hard drive of 160 GB and only one GB of memory. The remainder is similar to the 20" entry line machine, with the Geforce 9400M that plays the role of the conductor of the orchestrates and integrated video. Until it is available on the French education Store éducation, you will be able to check his existence in a PDF.
In practice, the price difference with the entry-level iMac is weak, and it will really only interest those which will set up a cluster of many of these machines.