Tomcat 5.5.27 is included in the package repository - if you're running either 2008.05 or 2008.11, then it can be installed with "pkg install SUNWtcat" (yes, the name of the package is an issue and is in the process of being addressed).
Note that the name of the package could be determined by doing a package search: $ pkg search -r tomcat -- This message posted from opensolaris.org
