Module development and code questions

If you are new at drupal module development, here is a good book to get you started. It helped me a lot.

http://www.drupalbook.com/

i want to convert the mail module of my website which is in 4.7 to the 5.1

is there any way for this

I asked this question in the general area and didn't get a response then realized it was probably because I asked in the wrong place. Sorry in advance for the duplicate post.

I'm writing a menu hook and I want to get the current path so I can create a dynamic menu from it. I've found two ways of getting it thus far:

$local_path = str_replace(base_path(),"",request_uri());
$local_path = substr(request_uri(),strlen(base_path())) ;

Does Drupal cache permissions? If so, how can I clear that cache for a
particular user at a particular time?

I have a module, og_user_roles
(http://www.drupal.org/project/og_user_roles), which adds group roles to
the $user object when it is loaded. So, when function "user_access"
executes, my module looks to see if the user is in a group context, and
if so, adds whatever role(s) the user might have within that particular
context.

Hi!

I'm not exactly proficient in Drupal's API, but I would like to add something onto the Contact module for my site (and if it works well, submit it for the next Drupal release) that allows the category to be preselected for the user via an argument passed from the URL.

So, like, mysite.com/contact/feedback would bring up the Contact form with the Feedback category already selected for the user. I don't want it to be locked as the Feedback category--the dropdown box should still be there--but Feedback should be preselected.

Hey all. I'm looking to implement a site that allows users to download various sets of data (each one dependent on the previous), process the data, then upload their results. The data itself is in a form of xml of which a design is currently in progress (by a significant person in the field I work in). I'm not looking to process the data within Drupal, it's not suited for web server class hardware. I just want to use Drupal to collect it.