The POWER5 processor is a 64-bit workhorse used in a variety of settings. Part 1 of this Assembly language for Power Architecture series is an introduction to assembly language concepts and the PowerPC instruction set. The series as a whole will introduce assembly language in general, specifically language programming for the POWER5.
A nice introduction on using assembly with as.
Some nice resources at the end of the Article one of witch is http://www-128.ibm.com/developerworks/linux/openpower/ : a way for linux developers to port their applications to linux Power/PowerPC, that is very nice.