PPC G5 Clustering ? XGrid? applications ?

I was wondering about building a cluster the other day. Then I stumbled acrost the Question "what could I do with somthing like this?". After this I Scoured the internet looking for apps or simulators that i could run on a cluster. So my question is, what could I do with a cluster ??? I dont really program in java or solve huge algorithms.... so far simulators look interestig But where could i get one??????😕

Four g5 ppc , 160 GB HD , dual 2.0 Ghz, 512 mb ram ???