bryce does use both cpu's(or either it is emulated in the nt based kernel) as the one guy running bryce and lightning on the same system.. it probaly lowers you render speed.. taking up more video and real memory than than needed.. my dual p2's @ 333 renders about 25% faster then my amd 750 with the process set in below normal mode.. in real time mode that figure goes up some .. but not by much.... as far as running bryce and lightning on the same comp.. i have never tried it .. i am just basing my remark from running multiple instances on a dual processor machine and spliting them apart and running each instance one each processor which has always givin lower marks then running one instance on both :)