The CGI module is definitely the way to go! It will unencode form data, automatically deal with GET and POST data and a multitude of other things (that are very tricky to write yourself!) You can get good info on using it from "perldoc CGI". As to taint mode, you probably can't do better than "perldoc perlsec". Someone will probably give you some examples in their reply, but you should really read the docs mentioned above; there are good examples there.
chas
(Update: Lincoln Stein (the creator of CGI.pm) has written a book - "Official Guide to Programming with CGI.pm" (Wiley Publ.) which is very informative and easy to read. Also, Ovid has a Web Programming Course linked from his home node which is very nice! You can probably find everything you need to know there.)