IP/~user problems (mod_rewrite)

[Vertigo]

Having issues getting my mod_rewrite working properly. Heres the htaccess...

RewriteEngine On

RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ dispatch.php [QSA,L]

Pointing the browser to http://www.domain.com/ is perfect, but browsing to http://IP/~user gives the following...

Not Found

The requested URL /home/<user>/public_html/dispatch.php was not found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

with error log....

File does not exist: /var/www/html/home
File does not exist: /var/www/html/404.shtml

any idea how to get it working for both access methods?