There are better places to ask about OC, you might try
XtremeSystems Inc
the good news is most of the advice here is correct.
I do need to ask a few questions for your consideration:
1) how will your big screen connect to the computer?
I recommend HDMI over DVI as it carries audio, this will affect your video card purchase. Any of the newer cards will play movies at 1080P.
2) if you are fresh at OC'ing be sure to read up on cooling first and be very cautious. Basically you are fighting heat when you OC more than anything else
3) you will OC your CPU and RAM separately, each has a different effect on the system depending on where your bottlenecks are. In my case 1604 on the RAM at 3.6 GHz on the CPU is faster than 1403 on the RAM and 4.0 GHz on the CPU.
4) keep CPU-Z by your side at all times, Win7 has a nasty habit of resetting the number of cores if it crashes. Reenable them by clearing the tick for number of processors under msconfig/boot/advanced
5) consider running XP 32 bit, you will probably be reinstalling a lot and there is a lot of support for OC with it. If you go Win7, go 64 bit and at least Pro.