Hello Roberto,
I am trying to figure out why it does not work, but it is the first time I'm trying to include the servlet, so I'm basically trying to go through all the installation steps, and I see that the program assembly.sh does not exists in the WAS 6.1 standard installation!!!
Well, after some research I've found that maybe you need to install the Websphere Application Server Toolkit!
I will keep you informed on my findings.
But in all cases, if you find problems like that, I can only advise you to open a PMR with IBM, and explain you are trying to follow the documentation to deploy this servlet and it does not work.
Then, if it is a documentation problem, then it will be corrected, but in all cases you will receive the correct procedure with all prereq in order to deploy this servlet in your configuration.
I don't know if it helps, but if you have such problems, please for everybody, open a PMR, so it will be corrected for the future users!
Cheers,
Alessandro