we have i7 + xp64 and cs4 makes constant pain in ass - first we had no luck to launch AFX and PPro - they crashed on startup.. then we disabled some io plugins and they started to run, however we were not able to use Encoder.. so we switched back to cs3, which is more stable, yet still we do encoding on another granny P4 workstation.
seems that Adobe does not care about 64bits, at least i couldnt find any fully working solution yet. vista could be solution, but then you should think that great percentage of resources will be consumed by vista itself.. cant wait for win7 and its compatibility.