Generalising URLs in a WPMU?

Hello -

A man's life depends upon this piece of information.

We're in the WPMU realm. Now If I wanted to place a link to "adding a new post" on the home page of the main site, so as to direct individual users to new post pages in their own blogs, what link can I use?

Like, how can I generalise the username in blog, because that is the only piece of information that is different.

given his username is myrtlebeach, link becomes
http://xxx_dsfdsf.com/myrtlebeach/wp-admin/post-new.php

can I generalise this:
http://xxx_dsfdsf.com/%username%/wp-admin/post-new.php and make this a link?