.htaccess code -n- ../ jumps; httpd.conf

[anshul]

i've few questions.

suppose i've many sub_domain in my 'www' folder.
these domains relate to different users.
one domain corresponds only for one particular user.
i want2ensure that some users cannot use files out of their
address, i.e., sub_domain.mydomain.com
( they are allowed to use files -n- folders within their sub_domain folder )
i want2ensure that some users use files out of their
address, i.e., sub_domain.mydomain.com, for only a particular
folder above or a list of folders above or a paricular file above
or a list of files above. etc. etc.

next thing is that suppose i've address:
[my_sub_domain.mydomain.com...]
that corresponds to a folder named 'my_sub_domain' in 'www'
i want2jump or refer files outside of this folder using
../ scheme not [~...] e.g., <IMG src="../main_image_folder/logo.gif">
not something like: <IMG src="http://mydomain.com/main_image_folder/logo.gif">

other i've either make copies of each e.g., css and image
folders4each sub_domain or use fully qualified url in my code.
i don't prefer any of these method.

i appreciate any useful reply. thanx.

my webhosting company told me i can't access httpd.conf file; is these tricks possible by writing few lines2.htaccess file