The 43p 150 will support AIX levels from AIX 4.3.2 up to AIX 5.3.
If you decide to go for a later level make sure your firmware is up to date before you try the AIX install.
For firmware and AIX fixes - even the latest AIX 4.3.3 updates are still available:
IBM Support: Fix Central
Start with the product group of system p.
If you have the disks then load up 4.3 and have a play.
The AIX 4.3 command reference is no longer available on the IBM web site, as far as I know, but this site has a copy (and is much faster then the IBM site anyway):
AIX Version 4.3 Base Documentation
Have fun, oh, and welcome to the world of unix, I hope you enjoy your experience.