The CI user guide suggests this as a .htaccess to redirect all incoming traffic to index.php (except for direct requests, images, and robots):

[text]
RewriteEngine on
RewriteCond $1 !^(index\.php|images|robots\.txt)
RewriteRule ^(.*)$ /index.php/$1 [L]
[/text]

…which barfs on windows installs (I happen to be Windows, Apache, MySQL and PHP, but not using a WAMP package).

Removing the leading slash on the rewrite fixed it.

[text]
RewriteEngine on
RewriteCond $1 !^(index\.php|images|robots\.txt)
RewriteRule ^(.*)$ index.php/$1 [L]
[/text]