Module development and code questions

I am using the mudule "Embedded Video Field 5.x-1.x-dev".I set a label in a content type.I wanna make the field must be filled before user can submit the post.Such as the tiltle.I have installed cck module and views module.Thanks for your help!

We are developers of Drupal Ajax IM module : http://drupal.org/project/ajaxim
We would like to consult with Drupal community about problem we have faced:
At first Ajax IM server was developed as Drupal module, which is enough for 5-10 users, but can be too slow for more. The solution was to write a standalone server. Our customers wanted this server to be written in Ruby. Here is the question:

I've been doing a little work with the Texy! filter, as the Czech quotes were annoying me. I'd made the necessary alterations to include a "locale" (as Texy!'s api calls it) setting in texy_admin_settings(), but when these settings are actually submitted I want to have it clear out the cache_filter table (ie 'delete from cache_filter').

Is there some kind of hook, meta-hook, or hook trigger I can use for this? I'm looking for something I can define in the module itself.

Hi,

I'm creating a new Drupal site which will sell access to information. When clients make a purchase they can buy; a box with the information printed which will be shipped, a CD which will be shipped to them or access to a file download as a PDF. Each version of the product is priced differently. Is it possible to sell just one product and have these three as purchasing options?

I need two comment options for a single node, one with "comment" topic and another with "diary note".
How should i implement it ??, any suggestions....
Thnx in advance.

Shwetank

Hey there. Here's an extract from my installation instructions for a module I'm developping: