Buy an mb2300 board from keil. After that examine the arm architecture and the datasheet of lpc2378 (NXP chip) ROUGHLY. Dont waste time by diving in deeply. And begin to examine sample programs. After that put a project infront of yourself for TRADING PURPOSE (for manufacturing. and for selling). Life is not so long, go on with a serious project. Dont play around with details.
You want to build it yourself? With a homemade PCB? Good luck. The ARM is a TQFP puddle of fun to solder, epically on a PCB with no solder mask. Buy a prebuilt one like LPCeb2000. **broken link removed**