Basic Question on input to PostgreSQL
createdb is a commandline tool which should be run in a Windows commandline window ("Start -> Run -> "cmd.exe"). You have to have PostgreSQL's bin directory in the windows PATH in order for this to work without supplying the full program path.

As an alternative you can run SQL statements using the program psql (which is also a command line program).  You probably also have a start menu entry in the PostgreSQL folder name "SQL Shell" (or something similar) which starts psql directly. 

A list of GUI tools (apart from pgAdmin) is available in the Community Guide to PostgreSQL GUI Tools.