The typical way of doing this is to use apache's mod_rewrite to redirect requests to the url w/ parameters. Many, many applications do this to create 'human readable' and more search engine friendly urls.
For example, you might add this rule to make action=sales&year=2009 look like sales-2009.htm:
RewriteRule ^sales-2009.htm?$ index.php?action=sales&y=2009 [L]
When the user goes to 'sales-2009.htm', its actually redirected to the php page with the appropriate parameters. To the end user, though, it still displays sales-2009.htm in the browser's url bar.
You can, of course, use regular expressions w/ mod_rewrite, such that you can make the redirections much more flexible. You could, for example, make a single expression in the above example that would map any year to the correct parameter.