apache2 - accessing a directory from the web

[pianomatrix]

Ok, so here's a completely nub question. I'm trying to install joomla on my ubuntu server. So I have var/www/joomla as the location. My default page is at var/www/apache2. I want to access the joomla page by typing www.mydomain.com/joomla.
I went into /etc/apache2/apache2.conf and added the line
Alias /joomla /var/www/joomla.
However, I still can't access this page from my browser. http://localhost/joomla does display the page, but www.mydomain.com/joomla does not display the page.
What completely obvious step am I missing ?

[jledhead]

http://localhost/joomla does display the page, but www.mydomain.com/joomla does not display the page.
What completely obvious step am I missing ?

so the first part works but not the second part. what do you get if you type www.mydomain.com and what happens when you type www.mydomain.com/joomla

[pianomatrix]

When I type www.mydomain.com, I get the apache homepage "It works!".
If I'm working from the server, www.mydomain.com/joomla gives the correct joomla page (a recent discovery).
If I'm working from any other computer, www.mydomain.com/joomla gives "this page cannot be found" after 5 minutes of trying to connect.

[jledhead]

so from any other computer, if you type www.mydomain.com does it also return page can not be found?

if so then it sounds like a dns problem

[pianomatrix]

I just found the problem. I seriously can't believe this.
It turns out, it was a problem with my ie 7.0 on the other computer. I reset the cache, browsing hist, etc., and now it displays the page perfectly.
Thank you everybody for you help!