simple rewrite rule; need help!

Hello,

I'm working on adding url rewriting to my site and I have read a number
of tutorials on the subject. However, what I thought would be a
relatively simple task turns out to be a pain in the arse. This is
probably due to my not understanding the subtleties of url rewriting.

I'm working off my local server and Apache is properly configured.

The local site url is thus http://localhost/henri/

I want to rewrite design.php?cat=screen as design-portfolio/websites.html

so my .htaccess has the following:

Options +FollowSymlinks

RewriteEngine on
RewriteBase /henri
RewriteRule ^design-portfolio/websites\.html$ design.php?cat=screen [L]

I've modified the link to href="design-portfolio/websites.html".
However, when I click it I get a 404 not found (The requested URL
/henri/design-portfolio/websites.html was not found on this server)
which is right but I thought the purpose of this whole thing was to use
design-portfolio/websites.html as some sort of alias to
design.php?cat=screen

Can anyone help me understand what I'm doing wrong?

Thanks