Step 1: How to tell if your console is able to be jtagged/exploitable. To be able to jtag an Xbox 360 console, you have to have a kernel of 7371 or lower. If the kernel is any higher, you will not be able to jtag your xbox. To check if your xbox is exploitable, open up the system info tab under the dashboard.
Let me have some input instead of someone screaming at you, you are going to need a mod chip to do the RGH 1.2 expolit. The most cheapest way is to get a Coolrunner rev C (RGH modchip) and a JR-programmer v2 & USB cable (for the nand read/dump) However you are going to need to be able to solder VERY small points on the bottom of the mobo which in turn could break your Xbox if done wrong, if yo have any doubts use a RGH service.