Hi, i am building a computer but getting a bit confused with the DVD drive. i know i need a sata cable which i have already ordered but do i need a power cable as well?

I thought the only cable i need is the sata cable, here is the one im using: http://www.amazon.co.uk/SATA-POWER-ADAPTER-CABLE-DATA/dp/B000ITL1PG/ref=sr_1_1?ie=UTF8&qid=1289035292&sr=8-1

do they both plug in or do i only need one? thanks