Hi, Mike, and welcome to LQ!
I'll start with the easy question- If you can find it here
, it's free. Just download, burn the image to CD, boot from CD and install.
The CPU on the RS/6000 7025-F40 only ranged from 133-233MHz. That's pretty slow in today's world. The only suggestion I have is to try a light-weight distro like DSL or Puppy.