it's okay!
is that one for the 550/ gigabit ethernet model?
Yes, there were several models of the G4 PowerBook that used the same case design, and those instructions should work for yours. It's easy enough to tell by seeing if the instructions and diagrams match what you see on the outside of your G4 before you start.
What I think the problem with the RAM is that there is not enough.
While that's certainly true, it would not cause the 3 beeps you are hearing at startup. That's a bad/unseated RAM or logic board issue, as jchuzi suggests.
