Apple is now Shipping the Mac Pro which replaces the PowerMac G5
it uses Dual Dual Core (quad core) Intel Xeon “Woodcrest” Processors at 2Ghz, 2.66Ghz or 3Ghz and all systems include 1GB of RAM
A quad 2.0Ghz with 1GB of RAM and 160GB HD and 16X DL Superdrive (DVD burner) is under $2,200
Now while not cheap it is slightly less than a similar equipped Dell Precision workstation (although im sure you can build your own machine for much less it wont run OS X 
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