Maybe you can help, Global variables?

[eluser]Chad Fulton[/eluser]
This seems very odd to me. I would suggest you figure out how to fix the ISAPI_REWRITE problem with AJAX, since it may kick up other bugs at some point.

However, if you really want to do it this way, then I suggest extending the URL Helper to have a new function that does what you want. It could be called something like index_url()

Here's how you might do it (although, if you don't have a firm grasp of extending helpers, you might check out that link above anyway!):

application/helpers/MY_url_helper.php

Code:

function index_url() {
    return base_url().'index.php/';
}