I don't know about the url parsing, it'll be in the bbcode functions somewhere.
The attachments is fairly easy if you know how to hack the templates. Assuming the site you mean is your url (i.e. vb 3.0) open the postbit template, find
Code:
<if condition="$show['attachments']">
and replace with
Code:
<if condition="$show['attachments'] AND $bbuserinfo[userid]">
That will only show the attachments to logged in users