mod_rewrite problem

I've never used mod_rewrite before and I'm having the hardest time getting it to work. It is installed and running.
Here is my .htaccess file

RewriteEngine On
RewriteRule ^.*a.php$ /t.php [L]

I've tried every different variation on this that I can think of. Not matter what I get the following in the error log.
script not found or unable to stat.

The url that I'm using to test this is
http://localhost/~bloc/modr/a.php