Have to agree (again) with Naples.
I would always personally go for P4 but it really depends on how much heavy (graphical) work you intend doing, not just viewing digital pictures. However I have found that using the faster celerons they do manage the job.
Look at the AMD Xp options as in the past I have found that a few months down the line you can usually swap the processor for something newer, Intel chips have caused more problems in this area, so again it depends on how into your computer you are going to get.
Have you considered building your own PC as this can also save you a few coppers in the long run, though it is sometimes a better idea to get the shop to do it. Though there is nothing more satisfying than transforming that pile of bits into a working PC. That does make me sound quite sad - wife is right I need to get out more.