Strange URI behavior

[eluser]gentleJuggernaut[/eluser]
I have just set up CI 1.7.

When I go to the base of my site I get the welcome page as expected.

http://localhost/

When I try to go to the controller I get a 404 page not found error.

http://localhost/welcome/

Now the odd thing is that when I put a ? in front of the controller name it works as I would expect just the controller name to work

http://localhost/?welcome/

I am not really clear on how the .htaccess file works, so here is what I am currently using (from the URI page of the CI manual):

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


I dug around and found some topics that were similar and they suggested putting a ? at the end of the index.php reference in the .htaccess file, so I have also tried this (with no change in results):

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


I have set $config['base_url'] to the base of my site
I have set $config['index_page'] = ""
I have left $config['uri_protocol'] = "AUTO"
I have left $config['enable_query_strings'] = FALSE

Any ideas?

Thx.