The Intel P4 doesn't run faster than the Centrino just because the processor speed seems faster. In fact, the 1.5Ghz Centrino's I have worked on have seemed faster than the 3Ghz P4 laptops.

There is a major difference in how the processors work, the amount of cache and other changes make the Centrino a lot faster than the Ghz ratings appear to show.

It doesn't matter what broadband service you get, they will all work with 802.11G, it's dependent on the router or access point you purchase. BUT...you only use the faster speeds for file sharing, not for Broadband, since the fastest internet connections are in the 6Mb range while 802.11b runs at 11Mb. Most home users are only running 1.5Mb at this time.