Arachnophilia is a source-code editor written in Java; it handles several languages such as Perl, Java, HTML, XML... Please be sure to read the homepage carefully, though, as there are restrictions on modifying the program. It might serve to give you some ideas, though... You might also try The Code Project, or have a look at extending/modifying our very own PerlMonks Editor, by GrandFather.

Something else that might help is Super Searching for "syntax highlighting", or have a look at code2html.

HTH,