Dot is distributed by AT&T Bell labs and is available for restricted use. It can be obtained via anonymous ftp or via WWW access. Dot is actually included in a package of four graph visualization tools. The other tools are called dotty, neato and tcldot. You can obtain a non-commercial license for dot/dotty/neato/tcldot and download the software from the Web page:
http://www.research.att.com/sw/tools/graphviz
Choose source or binary (executables are available for some common Unix machines and for Microsoft Windows). If you accept the non-commercial license, download the 'graphviz' package.
Our experience with dot is very limited. Thus, we will not be able to help you install it. Hopefully, installation should be fairly straight forward.