Better to use lj-user-ex plugin instead - it has the same syntax as native livejournal markup.
Replaces <lj user="username"/> and <lj comm="community"/> with correct HTML code. Supports both <lj user="username"/> and <lj user="username"> forms, plus communities.
Although it can't be found when simply searching in wordpress plugins search. Damn those ass-hands.
Really sorry for author - but it's really better to use that one.
It is already old, but can't be broken - there's nothing to be broken.
By the way, it's not advertising, I'm not the author of LJ user EX ^^