I think go with Sempron
I have used a lot of intel and amd processors. Each one has its own good and bad. I think that the sempron is the better choice because it works generally better and the most important thing (please correct me if I am wrong) it has the powernow technology. The celeron m does not have the speedstep (or something like that) that the pentium m has. that was reserved for the centrino marketing. that means that the centrino will consume more energy. save the money for a bigger and 5400 hdd.