You did not mention a price limit, but I always build mine top of the line with no limits if it's a PC. However, the Mac Pro is great for duel-booting. You do not have to use Boot Camp on the same hard drive. It is possible to use two dedicated drives and simply select the OS you want on system boot.

If you are wanting PC only and not interested in the top line Nehalem CPUs that are only available right now on the Mac Pro then I would do:

1. Coolermaster ATCS 840 case.

2. Corsair HX 1000 Silencer Power Supply.

3. Corsair Dominator 12GB or more RAM.

4. i7 975 CPU.

5. LG Blu Ray Burner/DVD/CD.

6. Corsair H20 liquid cooling system.

7. Corsair 256GB SSD - 2X in Raid 0 configuration - 500GB for your OS and main apps.

8. 2 2TB Western Digital HD "Black edition". For data, photos, movies, etc.

9. EVGA nVidia 295 graphics card. or 2 nVidia 285 cards in SLI.

10. EVGA X58 SLI i7 motherboard.

11. Zalman high performance case cooling fans.

12. Windows 7 64 bit Professional or Ultimate.

13. Overclock to 4Ghz easily obtainable to be stable. Overclock graphics card. Custom heat sensors with external display in 5.25 drive bay, shrink tube and tidy wiring.

Jeff

Development on: Mac Pro 2008, Duel-Boot OS - Snow Leopard 10.6.6 & Windows 7 Ultimate 64bit, 2 x 2.8 GHz Quad-Core Intel Xeon , 10GB 800 MHz DDR2 RAM, NVIDIA GeForce 8800GT.