Apple dropped the IBM PowerPC chips because the PowerPC roadmap wasnt what they wanted. Intel has some SICK chips in the works that consume far less energy than the chips of today, and also feature a 45nm manufacturing process which will allow even more system bandwidth than the PPC chips we have in macs today.

OSX 10.4 can and will run on any x86 machine...however apple is expected to launch OSX 10.5 Leopard along with the Intel-Macs which will ensure that the Mac system will remain a closed source.

So what advantage will apple have on other x86 machines in the future? Lets not forget how much you pay for a mac and how well it runs. HP, Dell, and Gateway will most definitely not be utilizing the higher-end x86 offerings from Intel. Expect dual-core powerbooks, ibooks, and mac mini's running dual-core 2.0ghz chips in mid 06, with imacs and powermacs following close behind.

BTW, OSX 10.5 will support both PPC and x86 systems for many many years to come. My advice would be to purchase one of the final revision PPC Macs, as the first few generations of Intel-Macs are likely to be buggy.