+1 for MykC's build - very hard to beat for the price.
You could just get a 750TX for $20 more than the 650TX and get rid of the adapters. It may actually be cheaper if the shipping charge for a $3 adapter is $8.
(OK, I have no idea how much the shipping is...)
You can buy the adapters later when/if you add a second HD 4870. The 650TX doesn't need any adapters for the first HD 4870. It only needs them for the second one.
If you don't intend to overclock you can skip the Xigmatek cooler. The stock fan on that X3 720 CPU is good enough for its intended usage i.e. that CPU at stock clocks.
I'd suggest adding Vista Home Premium 64-bit OEM to the mix, and a 22" monitor (or 24", if possible).
Edit: between E8400 and X3 720 - I don't think you'd notice a difference, except for FSX or GTA4 where the third core gives the X3 720 an advantage. If you play those games you should probably consider a quad, like Phenom II 920 or Q8200.