It is possible to install Geforce 8800 GS in an old iMac

The lastest iMacs have faster processors, a swifter memory bus, but they have especially the possibility of being equipped with Geforce 8800 GS (actually a 8800 M GTS), video card with the new performances for this range of Apple.
It is not officially possible to change the video card of a iMac, however one of the members of our forums, "loloternet" who is an Apple certified technician, succeeded in grafting such a card into an iMac of the preceding generation.
The thing is thus realizable. Alas, this card is in theory available only via 'after sales service' and an exchange requires the disassembling of the iMac, which is a delicate thing even for a professional.
Let us wish that in future Apple takes into account the modularity of the iMac to be able to change the hard disk, or, and why not, the video card (one can always dream).