Problems to add a form in a block
More information would be more helpful to answering this question. I have no idea what file/function you have put this code into, if you have in your module any of the other hooks necessary to display a block or what your actual end-goal is here (are you printing a form in a block created by another module?). However, this code doesn't seem to correlate to any of the hooks necessary for creating a block within a module in Drupal 6.

You should take a look at the Examples for Developers module and its examples of a module that creates a block and a module that creates a form. By following those examples, you should be able to easily build a module that will create a form and a custom block that outputs that form.