For Tomcat 6 You'll want this link http://tomcat.apache.org/download-60.cgi and probably one of the binary distributions. I believe both Windows and Linux are included in the same zipped files, i.e. Linux uses shell script and Windows uses .bat files in order to start tomcat.
For installing you can read the documentation from each site, but for linux I like to use http://www.howtoforge.com . They really have a great community and plenty of installation walk-throughs.