My pc now runs debian.
Thanks again to Joel for the Knoppix advice: that was the very base for me. I wouldn't have dared to make any move without that lifesaver cd.
I then tried and burned many different disks from the debian site (and others): they all went to the rubbish bin after some weeks and many efforts.
Thanks to Jade:
"There are a lot of alternative ways of installing debian, though, so sometimes people who think Debian is hard to install just haven't tried one of the easy ways..."
I looked for something easy and found it at the end: Libranet.
You just start Knoppix, download Libranet 2.7 and a few minutes later debian is installed.
They say it is 100% debian woody: I do not know how to check myself, so I trust them.
Now it is time to try and see whether there is a way to install OpenACS.
I recently gave a look an the documentation: very complicated, convoluted, lots of different software, far from being easy. I will try, anyway.
If somebody knows of an easy way to install OpenACS, please let me know.