Want to build a new PC for capturing and broadcasting HD media

Hi goose,
I don't know a whole lot about the subject, as i've never really needed to (<3 mouse and keyboard for gaming) But I will help you best i can.

We should probably look at an h67 board since you want to video edit.
The i3-2100 is ideal, but if you can stretch the budget grab an i5-2400.

I would also grab a sizable HDD, probably 1-2 terabytes.

I don't know what you plan to use in editing, but some programs prefer NVidia so let's play it safe.
Get a GTX 560 (ti if you can fit it) for gaming and rendering muscle.

4gigs of ram will be plenty, but try for 8GB if the budget allows.

Lastly, please fill this form. Makes it easier for me and the other members to help you: http://www.tomshardware.com/forum/261222-31-build-advic...

I apologize for lack of links, I can't access a whole bunch of links at this time.

The hardware requirements for that card are pretty steep.

Basic Requirements
http://www.blackmagic-design.com/support/detail/support...
Graphic Cards
http://www.blackmagic-design.com/support/detail/support...
Disk Arrays
http://www.blackmagic-design.com/support/detail/support...

a forum discussion on the Raid requirement
http://forum.videohelp.com/threads/313441-Black-Magic-I...

if you are only trying to do 720p uncompressed, you should be able to get away with using just the MB raid controller. you will need a boot HD for the OS, and a separate Disk for capture (RAID 0)

Do have any hardware already: monitor, KB,Mouse, DVD, case, psu?
how about the OS (WIN7)?

I have the black magic right now and i'm using it. I can record but i can not stream with it as my computer doesn't have the power to do so.

I'm sure i could go and buy all the parts i need and through together a computer that could do it, but i don't want to miss something or pay way more than i would need to.

The community would be glad to assist you, but you need to fill out he Form that striker410 linked so that we know what stuff you already have and what you need the system to do. so far I think you need a design that has:

Quad Core CPU (the manufacture's recommended board seem to favor Intel CPU's)
MB that Support the PCIe x1 card (Gigabyte or ASUS seem to have the bios support) and has a raid controller on it. (no Crossfire or SLI)
4 GB ram
a mid range GPU
a small system drive (boot drive)
a Storage drive (large 1-2 TB)
as Scratch drive most likely 2-3 x 500 GB drives for RAID 0 for streaming uncompressed video capture.

what we need to know is, Do you have a:
monitor
KB
Mouse
OS
Case

Filling out that form will help us help you.