[support] Simple Module Coding Question

[Fred Jones]

I have a menu item whose callback is drupal_get_form, but in the form
function, I would like to know what arguments follow my path. What I
mean is that my menu path is:

custommod

and the actual URL I am calling is

custommod/3

and in the form I want to be able to see that 3. Is this available in
the API? I tried making my callback a custom function and then using
drupal_render to render my form at the end of that function, and while
then I see the 3, the form came out all messed up--it was out of order
it seems. Is this the right way to do it? Or is there something I am
missing?

Thanks!