Solr3 and solr4 side by side in tomcat on windows

[Gian Maria Ricci - aka Alkampfer]

Hi to everyone, I've a solr3.6 server up and running, now I wish to install 
solr4 on the same machine and if possible in side-by-side configuration. 
(tomcat on Windows) Is it possible and is there some documentation on how to do 
this? Thanks a lot. Gian Maria.