Grid computing can be used for high performance computations. However, a serious difficulty in concurrent programming of such heterogeneous systems is how to deal with scheduling and load balancing of such systems which may consist of heterogeneous computers on different sites. Distributed scheduling schemes suitable for parallel loops with independent iterations on heterogeneous computer clusters have been proposed and analyzed in the past. In this article, we implement the previous schemes in MPICH-G2 and MPIg on the TeraGrid. We present performance results for three loop scheduling schemes on single and multi-site TeraGrid clusters.