The only options really are:
Stick with the G5.
Buy a magma chassis ($$$$$).
Upgrade the PCIx cards to pcie and buy a mac pro ($$$).
Move to PC and windows (
)...My build consists of:
Gigabyte GA-P55-UD3 motherboard ($76 on ebay).
Intel i7 870 2.8ghz quad core processor ($202 on ebay).
Nvidia Quadro 3700 512mb graphics card ($90 on ebay).
Antec Take 3 rack case with PSU ($200 on ebay).
500Gb 7,200 RPM hard drive ($85 new).
2x4Gb 1333mhz DDR3 ram ($60 new).
Snow Leopard retail version ($39 new from apple store).
Total: $752.00
It is the first computer I have ever built... it took a full day of tinkering and trial and error with iBoot and Multibeast (the tonymacx86 "hackintosh" installers) to get everything up and running, but it is working great! Everything is functioning as normal, except for the onboard audio and full "sleep" function accessed via the apple menu. Not a big deal. I don't use either of those... with some further tinkering you will be able to get them to work.
If I can do this, anyone can really... just make sure you choose components that are tried and tested with the version of OSx you want. There is plenty of documentation on the net about it. If you are going to use PCIx slots, you need to get a motherboard that has native PCI support - a lot of newer motherboards (particularly those that use sandybridge processors) have a PCIx to PCIe bridge. Protools HD PCIx cards will fit on the motherboard but will not work in those motherboards!
The iBoot process is simple. Simply change your motherboard bios settings to those listed in the iBoot tutorial, stick your CD with iBoot on it in your cd drive... wait for iBoot to load, then stick in your osx install DVD and install the operating system. Once installed, run the latest combo update, then Multibeast! Multibeast allows you to choose the kext files (mac equivilent to hardware drivers) for your system. There are a large number of DSDT's (predefined kext lists) on the net for most types and makes of motherboard. I simply downloaded the DSDT for the GA-P55-UD3 motherboard I have and installed it via multibeast.
Presto!
A PC running OSx.
One hint: I wasted 2 hours trying to figure out why my computer wouldn't boot with OSX after I had installed it. The problem being, I installed two additional hard drives in the computer, and it was looking for an operating system on the wrong drive. Inside BIOS you can select the priority order of your drives. Whoops!


Namely because mac-evangelists rarely move to the dark-side. 

(..... Lob Grenade Now !!!)

