Hi Jaime,
I am not sure about the official
word from Apache.org for the exact min hardware specs.
However, Tomcat is not a resource hungry product and the least specs I've worked on goes back to a server with pentium pro 200MHz & 256 MB of RAM and it never had any problems.
It all depends on the web application you are trying to run. Hardware specs would just be a wild guess. If you are really keen then perform load
testing of your applications.
Rahul..