Practical experience is will be hard
You can buy your self some cheap power4.
But on power 4 you will be able to play only with OS,
maybe some WPARs.
But this what is making this system architecture different is visualization and machine that would allow you to play with that is to expensive.
There is a lot of online trainings quite big bunch of them you can find here
Index of /systems/power/community/aix/AIX_Movies
Also on Youtube you will find a lot of good movies
I would start from that .
You should think about some training
Aix Jumpstat could be a good idea
IBM Course description: AIX Jumpstart for UNIX Professionals (Self-paced Virtual Class) - IBM Training - United States
Maybe your new employer can arrange it for you