Leveraging browser caching

I'm having problems using .htaccess to leverage browser caching, which would be an improvement to the speed of my site, as Firebug tells me.

Searching around I have found code which I have inserted into my .htaccess file.

The .htaccess file already contains the following:

<filesMatch ".js$">
AddHandler application/x-httpd-php .js
</filesMatch>

Which works.

When I add the following code to create the browser caching........

# Turn on Expires and set default to 0
ExpiresActive On
ExpiresDefault A0

# Set up caching on media files for 1 year (forever?)
<FilesMatch "\.(flv|ico|pdf|avi|mov|ppt|doc|mp3|wmv|wav)$">
ExpiresDefault A29030400
Header append Cache-Control "public"
</FilesMatch>

# Set up caching on media files for 1 week
<FilesMatch "\.(gif|jpg|jpeg|png|swf)$">
ExpiresDefault A604800
Header append Cache-Control "public"
</FilesMatch>

# Set up 1 Hour caching on commonly updated files
<FilesMatch "\.(xml|txt|php|html|js|css)$">
ExpiresDefault A3600
Header append Cache-Control "proxy-revalidate"
</FilesMatch>

# Force no caching for dynamic files
<FilesMatch "\.(cgi|pl|htm)$">
ExpiresActive Off
Header set Cache-Control "private, no-cache, no-store, proxy-revalidate, no-transform"
Header set Pragma "no-cache"
</FilesMatch>

......I get "Internal server error".

Help!!